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Page 1: [Eng]Advanced Training Concrete Part1 2009.0.1

8122019 [Eng]Advanced Training Concrete Part1 200901

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1

Advanced TrainingConcrete according to EN 1992

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Concrete Workshop

2

All information in this document is subject to modification without prior notice No part or this manual may be reproduced storedin a database or retrieval system or published in any form or in any way electronically mechanically by print photo printmicrofilm or any other means without prior written permission from the publisher SCIA is not responsible for any direct or indirectdamage because of imperfections in the documentation andor the software

copy Copyright 2008 SCIA All rights reserved

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3

983124983137983138983148983141 983151983142 983107983151983150983156983141983150983156983155

Materials 5 Verification by the partial factor method 5

Design values 5 Partial factors for materials (art 2424) 5

Concrete 6 General (art 311) 6 Strength (art 312) 6 Elastic deformation (art 313) 10 Creep and shrinkage (art 314) 11 Design compressive and tensile strengths (art 316) 11 Stress-strain relations for the design of cross-sections (art 317) 12

Reinforcing steel 13 General (art 321) 13 Properties (art 322) 13 Design assumptions (art 327) 14

Durability and cover to reinforcement 15 Environmental conditions (art 42) 15 Methods of verification (art 44) 16 Concrete cover (art 441) 16

General (art 4411) 16 Minimum cover c min (art 4412) 16 Allowance in design for deviation (art 4413) 18

Analysis models 19 1_Eurocode 19 2_Scia Engineer 19

Assignment of analysis model 19 Difference between Beam and Column analysis model 20 Example 21

Beam 22 0_Description of used example 22 1_Recalculated internal forces 22

Shifting of moment line 22 Moment capping at supports 24 Shear force capping at supports 26 Other calculation settings 27

2 Theoretical reinforcement 27 Calculation of longitudinal reinforcement As 27 Calculation of shear reinforcement Ass 32

3 Practical reinforcement 34 4 Checks 39

Capacity check 39 Response check 41 Detailing provisions check 43 Crack control check 44

5 Automatic member reinforcement design 46 AMRD by means of the setup 47 AMRD by means of the conrete data 51 AMRD by means of a reinforcement template 54

Column Design 57 Calculation Types 57

Axial compression only 57 No reinforcement required (NEd lt NRd) 57 Reinforcement required (NEd gt NRd) 58 Explanation of the number of reinforcement bars 59

Uni-axial bending 60 Uni-axial bending calculation (sum) 60 Uni-axial bending calculation (max) 60

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Concrete Workshop

4

Bi-axial bending 62 EC Theory 62 Iteration process for bi-axial bending calculation 63 Iteration process ndash Example 64 Optimization 67

Calculation methods Overview ndash Automatic design 68 Circular columns 68

Example 68 2nd order calculation 70

Eurocode 70 Criterion for 1

st or 2

nd order calculation 70

Taking geometric imperfections into account 71 Taking 2nd order effects into account 71 Overview 72

Scia Engineer 73 Example 74

Concrete Setup Overview 76 Basic Settings 76 Advanced Settings 77

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5

Materials

Verification by the partial factor method

Design values

Partial factors for materials (art 2424)

Partial factors for materials for ultimate limit states γ c and γ s should be used

Note The values of γ c and γ s for use in a Country may be found in its National Annex The recommended values for lsquopersistent amptransientrsquo and lsquoaccidental design situations are given in Table 1 These are not valid for fire design for which reference should bemade to EN 1992-1-2 For fatigue verification the partial factors for persistent design situations given in Table 21N are

recommended for the values of γ cfat and γ sfat

These values can also be found in the concrete setup

Note As one can see al factors related to the code are shown in green on the screen Bydefault the values of the chosen code is taken

The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particularclauses of this Eurocode

Note The values of γ c and γ s in the serviceability limit state for use in a Country may befound in its National Annex The recommended value for situations not covered byparticular clauses of this Eurocode is 10

Lower values of γ c and γ s may be used if justified by measures reducing the uncertainty in the calculated resistance

Note Information is given in Informative Annex A

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Concrete Workshop

6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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Concrete Workshop

8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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Concrete Workshop

12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Concrete Workshop

14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 2: [Eng]Advanced Training Concrete Part1 2009.0.1

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2

All information in this document is subject to modification without prior notice No part or this manual may be reproduced storedin a database or retrieval system or published in any form or in any way electronically mechanically by print photo printmicrofilm or any other means without prior written permission from the publisher SCIA is not responsible for any direct or indirectdamage because of imperfections in the documentation andor the software

copy Copyright 2008 SCIA All rights reserved

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3

983124983137983138983148983141 983151983142 983107983151983150983156983141983150983156983155

Materials 5 Verification by the partial factor method 5

Design values 5 Partial factors for materials (art 2424) 5

Concrete 6 General (art 311) 6 Strength (art 312) 6 Elastic deformation (art 313) 10 Creep and shrinkage (art 314) 11 Design compressive and tensile strengths (art 316) 11 Stress-strain relations for the design of cross-sections (art 317) 12

Reinforcing steel 13 General (art 321) 13 Properties (art 322) 13 Design assumptions (art 327) 14

Durability and cover to reinforcement 15 Environmental conditions (art 42) 15 Methods of verification (art 44) 16 Concrete cover (art 441) 16

General (art 4411) 16 Minimum cover c min (art 4412) 16 Allowance in design for deviation (art 4413) 18

Analysis models 19 1_Eurocode 19 2_Scia Engineer 19

Assignment of analysis model 19 Difference between Beam and Column analysis model 20 Example 21

Beam 22 0_Description of used example 22 1_Recalculated internal forces 22

Shifting of moment line 22 Moment capping at supports 24 Shear force capping at supports 26 Other calculation settings 27

2 Theoretical reinforcement 27 Calculation of longitudinal reinforcement As 27 Calculation of shear reinforcement Ass 32

3 Practical reinforcement 34 4 Checks 39

Capacity check 39 Response check 41 Detailing provisions check 43 Crack control check 44

5 Automatic member reinforcement design 46 AMRD by means of the setup 47 AMRD by means of the conrete data 51 AMRD by means of a reinforcement template 54

Column Design 57 Calculation Types 57

Axial compression only 57 No reinforcement required (NEd lt NRd) 57 Reinforcement required (NEd gt NRd) 58 Explanation of the number of reinforcement bars 59

Uni-axial bending 60 Uni-axial bending calculation (sum) 60 Uni-axial bending calculation (max) 60

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4

Bi-axial bending 62 EC Theory 62 Iteration process for bi-axial bending calculation 63 Iteration process ndash Example 64 Optimization 67

Calculation methods Overview ndash Automatic design 68 Circular columns 68

Example 68 2nd order calculation 70

Eurocode 70 Criterion for 1

st or 2

nd order calculation 70

Taking geometric imperfections into account 71 Taking 2nd order effects into account 71 Overview 72

Scia Engineer 73 Example 74

Concrete Setup Overview 76 Basic Settings 76 Advanced Settings 77

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5

Materials

Verification by the partial factor method

Design values

Partial factors for materials (art 2424)

Partial factors for materials for ultimate limit states γ c and γ s should be used

Note The values of γ c and γ s for use in a Country may be found in its National Annex The recommended values for lsquopersistent amptransientrsquo and lsquoaccidental design situations are given in Table 1 These are not valid for fire design for which reference should bemade to EN 1992-1-2 For fatigue verification the partial factors for persistent design situations given in Table 21N are

recommended for the values of γ cfat and γ sfat

These values can also be found in the concrete setup

Note As one can see al factors related to the code are shown in green on the screen Bydefault the values of the chosen code is taken

The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particularclauses of this Eurocode

Note The values of γ c and γ s in the serviceability limit state for use in a Country may befound in its National Annex The recommended value for situations not covered byparticular clauses of this Eurocode is 10

Lower values of γ c and γ s may be used if justified by measures reducing the uncertainty in the calculated resistance

Note Information is given in Informative Annex A

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6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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Concrete Workshop

8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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Concrete Workshop

12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Concrete Workshop

14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 3: [Eng]Advanced Training Concrete Part1 2009.0.1

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3

983124983137983138983148983141 983151983142 983107983151983150983156983141983150983156983155

Materials 5 Verification by the partial factor method 5

Design values 5 Partial factors for materials (art 2424) 5

Concrete 6 General (art 311) 6 Strength (art 312) 6 Elastic deformation (art 313) 10 Creep and shrinkage (art 314) 11 Design compressive and tensile strengths (art 316) 11 Stress-strain relations for the design of cross-sections (art 317) 12

Reinforcing steel 13 General (art 321) 13 Properties (art 322) 13 Design assumptions (art 327) 14

Durability and cover to reinforcement 15 Environmental conditions (art 42) 15 Methods of verification (art 44) 16 Concrete cover (art 441) 16

General (art 4411) 16 Minimum cover c min (art 4412) 16 Allowance in design for deviation (art 4413) 18

Analysis models 19 1_Eurocode 19 2_Scia Engineer 19

Assignment of analysis model 19 Difference between Beam and Column analysis model 20 Example 21

Beam 22 0_Description of used example 22 1_Recalculated internal forces 22

Shifting of moment line 22 Moment capping at supports 24 Shear force capping at supports 26 Other calculation settings 27

2 Theoretical reinforcement 27 Calculation of longitudinal reinforcement As 27 Calculation of shear reinforcement Ass 32

3 Practical reinforcement 34 4 Checks 39

Capacity check 39 Response check 41 Detailing provisions check 43 Crack control check 44

5 Automatic member reinforcement design 46 AMRD by means of the setup 47 AMRD by means of the conrete data 51 AMRD by means of a reinforcement template 54

Column Design 57 Calculation Types 57

Axial compression only 57 No reinforcement required (NEd lt NRd) 57 Reinforcement required (NEd gt NRd) 58 Explanation of the number of reinforcement bars 59

Uni-axial bending 60 Uni-axial bending calculation (sum) 60 Uni-axial bending calculation (max) 60

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4

Bi-axial bending 62 EC Theory 62 Iteration process for bi-axial bending calculation 63 Iteration process ndash Example 64 Optimization 67

Calculation methods Overview ndash Automatic design 68 Circular columns 68

Example 68 2nd order calculation 70

Eurocode 70 Criterion for 1

st or 2

nd order calculation 70

Taking geometric imperfections into account 71 Taking 2nd order effects into account 71 Overview 72

Scia Engineer 73 Example 74

Concrete Setup Overview 76 Basic Settings 76 Advanced Settings 77

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5

Materials

Verification by the partial factor method

Design values

Partial factors for materials (art 2424)

Partial factors for materials for ultimate limit states γ c and γ s should be used

Note The values of γ c and γ s for use in a Country may be found in its National Annex The recommended values for lsquopersistent amptransientrsquo and lsquoaccidental design situations are given in Table 1 These are not valid for fire design for which reference should bemade to EN 1992-1-2 For fatigue verification the partial factors for persistent design situations given in Table 21N are

recommended for the values of γ cfat and γ sfat

These values can also be found in the concrete setup

Note As one can see al factors related to the code are shown in green on the screen Bydefault the values of the chosen code is taken

The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particularclauses of this Eurocode

Note The values of γ c and γ s in the serviceability limit state for use in a Country may befound in its National Annex The recommended value for situations not covered byparticular clauses of this Eurocode is 10

Lower values of γ c and γ s may be used if justified by measures reducing the uncertainty in the calculated resistance

Note Information is given in Informative Annex A

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6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Concrete Workshop

32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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4

Bi-axial bending 62 EC Theory 62 Iteration process for bi-axial bending calculation 63 Iteration process ndash Example 64 Optimization 67

Calculation methods Overview ndash Automatic design 68 Circular columns 68

Example 68 2nd order calculation 70

Eurocode 70 Criterion for 1

st or 2

nd order calculation 70

Taking geometric imperfections into account 71 Taking 2nd order effects into account 71 Overview 72

Scia Engineer 73 Example 74

Concrete Setup Overview 76 Basic Settings 76 Advanced Settings 77

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5

Materials

Verification by the partial factor method

Design values

Partial factors for materials (art 2424)

Partial factors for materials for ultimate limit states γ c and γ s should be used

Note The values of γ c and γ s for use in a Country may be found in its National Annex The recommended values for lsquopersistent amptransientrsquo and lsquoaccidental design situations are given in Table 1 These are not valid for fire design for which reference should bemade to EN 1992-1-2 For fatigue verification the partial factors for persistent design situations given in Table 21N are

recommended for the values of γ cfat and γ sfat

These values can also be found in the concrete setup

Note As one can see al factors related to the code are shown in green on the screen Bydefault the values of the chosen code is taken

The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particularclauses of this Eurocode

Note The values of γ c and γ s in the serviceability limit state for use in a Country may befound in its National Annex The recommended value for situations not covered byparticular clauses of this Eurocode is 10

Lower values of γ c and γ s may be used if justified by measures reducing the uncertainty in the calculated resistance

Note Information is given in Informative Annex A

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6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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Concrete Workshop

8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Concrete Workshop

14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

8122019 [Eng]Advanced Training Concrete Part1 200901

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Concrete Workshop

16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Concrete Workshop

64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 5: [Eng]Advanced Training Concrete Part1 2009.0.1

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5

Materials

Verification by the partial factor method

Design values

Partial factors for materials (art 2424)

Partial factors for materials for ultimate limit states γ c and γ s should be used

Note The values of γ c and γ s for use in a Country may be found in its National Annex The recommended values for lsquopersistent amptransientrsquo and lsquoaccidental design situations are given in Table 1 These are not valid for fire design for which reference should bemade to EN 1992-1-2 For fatigue verification the partial factors for persistent design situations given in Table 21N are

recommended for the values of γ cfat and γ sfat

These values can also be found in the concrete setup

Note As one can see al factors related to the code are shown in green on the screen Bydefault the values of the chosen code is taken

The values for partial factors for materials for serviceability limit state verification should be taken as those given in the particularclauses of this Eurocode

Note The values of γ c and γ s in the serviceability limit state for use in a Country may befound in its National Annex The recommended value for situations not covered byparticular clauses of this Eurocode is 10

Lower values of γ c and γ s may be used if justified by measures reducing the uncertainty in the calculated resistance

Note Information is given in Informative Annex A

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6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

6

Concrete

General (art 311)

The following clauses give principles and rules for normal and high strength concrete Rules for lightweight aggregate concreteare given in Section 11

Strength (art 312)

The compressive strength of concrete is denoted by concrete strength classes which relate to the characteristic (5) cylinderstrength f ck or the cube strength f ckcube in accordance with EN 206-1

The strength classes in this code are based on the characteristic cylinder strength f ck determined at 28 days with a maximumvalue of C max

Note The value of Cmax for use in a Country may be found in its National Annex Therecommended value is C90105

The characteristic strengths for f ck and the corresponding mechanical characteristics necessary for design are given in Table 3All values can also be found in the material library of Scia Engineer

In certain situations (eg prestressing) it may be appropriate to assess the compressive strength for concrete before or after 28days on the basis of test specimens stored under other conditions than prescribed in EN 12390

Note test values can be inputted in the material library

If the concrete strength is determined at an age t gt 28 days the values αcc and αct defined in 316 (1) and 316 (2) should bereduced by a factor k t

Note The value of kt for use in a Country may be found in its National Annex Therecommended value is 085

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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Concrete Workshop

8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Concrete Workshop

14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Concrete Workshop

16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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Concrete Workshop

20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 7: [Eng]Advanced Training Concrete Part1 2009.0.1

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7

It may be required to specify the concrete compressive strength f ck(t ) at time t for a number of stages (eg demoulding transferof prestress) where

f ck(t ) = f cm(t ) - 8 (MPa) for 3 lt t lt 28 days

f ck(t ) = f ck for t ge 28 days

More precise values should be based on tests especially for t le 3 days

The compressive strength of concrete at an age t depends on the type of cement temperature and curing conditions For amean temperature of 20degC and curing in accordance w ith EN 12390 the compressive strength of concrete at various ages f cm(t )may be estimated from Expressions (31) and (32)

f cm(t ) = β cc(t ) f cm (31)

with (32)

where

f cm(t ) is the mean concrete compressive strength at an age of t days

f cm is the mean compressive strength at 28 days according to Table 31

β cc(t ) is a coefficient which depends on the age of the concrete t

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Concrete Workshop

8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 8: [Eng]Advanced Training Concrete Part1 2009.0.1

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8

t is the age of the concrete in days

s is a coefficient which depends on the type of cement

= 020 for cement of strength Classes CEM 425 R CEM 525 N and CEM 525 R

(Class R)

= 025 for cement of strength Classes CEM 325 R CEM 425 N (Class N)

= 038 for cement of strength Classes CEM 325 N (Class S)

This type of cement can be chosen in the material library

The tensile strength refers to the highest stress reached under concentric tensile loading For the flexural tensile strengthreference should be made to 318 (1)

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9

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10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

8122019 [Eng]Advanced Training Concrete Part1 200901

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

30

To take the user reinforcement into account the following setting has to be on (default it is on)

8122019 [Eng]Advanced Training Concrete Part1 200901

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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Concrete Workshop

38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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9

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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Concrete Workshop

12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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Concrete Workshop

20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

10

Elastic deformation (art 313)

The elastic deformations of concrete largely depend on its composition (especially the aggregates) The values given in thisStandard should be regarded as indicative for general applications However they should be specifically assessed if thestructure is likely to be sensitive to deviations from these general values

The modulus of elasticity of a concrete is controlled by the moduli of elasticity of its components Approximate values for the

modulus of elasticity E cm secant value between σc = 0 and 04f cm for concretes with quartzite aggregates are given in Table 31For limestone and sandstone aggregates the value should be reduced by 10 and 30 respectively For basalt aggregates thevalue should be increased by 20

Variation of the modulus of elasticity with time can be estimated by

E cm(t ) = (f cm(t ) f cm)03

E cm (35)

where E cm(t ) and f cm(t ) are the values at an age of t days and E cm and f cm are the values determined at an age of 28 days Therelation between f cm(t ) and f cm follows from Expression (31)

Poissonrsquos ratio may be taken equal to 02 for uncracked concrete and 0 for cracked concrete

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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Concrete Workshop

12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Concrete Workshop

14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Concrete Workshop

16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 11: [Eng]Advanced Training Concrete Part1 2009.0.1

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11

Creep and shrinkage (art 314)

Creep and shrinkage of the concrete depend on the ambient humidity the dimensions of the element and the composition of theconcrete Creep is also influenced by the maturity of the concrete when the load is first applied and depends on the duration andmagnitude of the loading

The creep coefficient ϕ(tt 0) is related to E c the tangent modulus which may be taken as 105 E cm Where great accuracy is notrequired a value found from a figure (Figure 31) may be considered as the creep coefficient provided that the concrete is notsubjected to a compressive stress greater than 045 f ck (t 0) at an age t 0 the age of concrete at the time of loading

Note For further information including the development of creep with time Annex B may be used

All these parameters can be inputted in the setup for concrete or in the beam concrete data

The creep deformation of concrete εcc(infint 0) at time t = infin for a constant compressive stress σc applied at the concrete age t 0 isgiven by

εcc(infint 0) = ϕ(tt 0) (σc E c)

Design compressive and tensile strengths (art 316)

The value of the design compressive strength is defined as

f cd = αcc f ck γ C (315)where

γ C is the partial safety factor for concrete see 2424 and

αcc is the coefficient taking account of long term effects on the compressive strength and of unfavourable effects resulting fromthe way the load is applied This value can also be found in the material library (see figure 10)

Note The value of α cc for use in a Country should lie between 08 and 10 and may be found in its National

Annex The recommended value is 1

The value of the design tensile strength f ctd is defined as

f ctd = αct f ctk005 γ C (316)

where

γ C is the partial safety factor for concrete see 2424 and

αct is a coefficient taking account of long term effects on the tensile strength and of unfavourable effects resulting from the waythe load is applied

Note The value of α ct for use in a Country may be found in its National Annex The recommended value is 10

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Concrete Workshop

12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 12: [Eng]Advanced Training Concrete Part1 2009.0.1

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12

Stress-strain relations for the design of cross-sections (art 317)

For the design of cross-sections the following stress-strain relationship may be used see figures below

εc2 is the strain at reaching the maximum strength in the parabola-rectangle diagram

εcu2 is the ultimate strain in the parabola-rectangle diagram

εc32 is the strain at reaching the maximum strength in the bi-linear diagram

εcu3 is the ultimate strain in the bi-linear diagram

The user can choose in the material library which one of the diagrams should be used for the calculation

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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Concrete Workshop

38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 13: [Eng]Advanced Training Concrete Part1 2009.0.1

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13

Reinforcing steel

General (art 321)

The following clauses give principles and rules for reinforcement which is in the form of bars de-coiled rods welded fabric andlattice girders They do not apply to specially coated bars

Properties (art 322)

The behaviour of reinforcing steel is specified by the following properties

- yield strength (f yk or f 02k)

- maximum actual yield strength (f ymax)

- tensile strength (f t)

- ductility (ε uk and f t f yk)

- bendability

- bond characteristics (f R See Annex C)

- section sizes and tolerances

- fatigue strength

- weldability- shear and weld strength for welded fabric and lattice girders

The steel properties can be found in the material library (see Figure 18)

The mean value of density may be assumed to be 7850 kgm3

The Eurocode applies to ribbed and weldable reinforcement including fabric

Note The properties of reinforcement required for use with this Eurocode are given in Annex C

The application rules for design and detailing in this Eurocode are valid for a specified yield strength range f yk = 400 to 600 MPa

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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Concrete Workshop

16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Concrete Workshop

32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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Concrete Workshop

38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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14

Design assumptions (art 327)

For normal design either of the following assumptions may be made

a) an inclined top branch with a strain limit of εud and a maximum stress of kf yk γ s at εuk

where k = (f t f y)k

b) a horizontal top branch without the need to check the strain limit

Note 1 The value of εud for use in a Country may be found in its National Annex The recommended value is

09 ε uk

Note 2 The value of (f t f y)k is given in Annex C

In the material library user can choose between assumptions a and b

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

30

To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Concrete Workshop

32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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15

Durability and cover to reinforcement

Environmental conditions (art 42)

Exposure conditions are chemical and physical conditions to which the structure is exposed in addition to the mechanicalactions

Environmental conditions are classified according to Table 41 see Figure 23 based on EN 206-1

In the concrete setup the user can choose the desired exposure class All items in blue can be overwritten in the data concreteon a member

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16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

16

Methods of verification (art 44)

Concrete cover (art 441)

General (art 4411)The concrete cover is the distance between the surface of the reinforcement closest to the nearest concrete surface (includinglinks and stirrups and surface reinforcement where relevant) and the nearest concrete surface

The nominal cover shall be specified on the drawings It is defined as a minimum cover c min (see 4412) plus an allowance in

design for deviation ∆c dev (see 4413) cnom = c min + ∆c dev

Minimum cover c min (art 4412)

Minimum concrete cover c min shall be provided in order to ensure

- the safe transmission of bond forces (see also Sections 7 and 8)

- the protection of the steel against corrosion (durability)

- an adequate fire resistance (see EN 1992-1-2)

The greater value for c min satisfying the requirements for both bond and environmental conditions shall be used

cmin = max cminb cmindur + ∆cdurγ - ∆cdurst - ∆cduradd 10 mm

where

c minb minimum cover due to bond requirement see 4412 (3)

c mindur minimum cover due to environmental conditions see 4412 (5)

∆cdurγ additive safety element see 4412 (6)

∆cdurst reduction of minimum cover for use of stainless steel see 4412 (7)

∆cduradd reduction of minimum cover for use of additional protection see 4412 (8)

In order to transmit bond forces safely and to ensure adequate compaction of the concrete the minimum cover should not beless than c minb given in table 42 (see Figure 26)

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Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 17: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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Concrete Workshop

20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 18: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

18

Allowance in design for deviation (art 4413)

To calculate the nominal cover c nom an addition to the minimum cover shall be made in design to allow for the deviation (∆c dev)The required minimum cover shall be increased by the absolute value of the accepted negative deviation

Note The value of ∆c dev for use in a Country may be found in its National Annex The recommended value is

10 mm

In certain situations the accepted deviation and hence allowance ∆c dev may be reduced (see tickbox in Figure 25)

Note The reduction in ∆c dev in such circumstances for use in a Country may be found in its National Annex

The recommended values are

- where fabrication is subjected to a quality assurance system in which the monitoring includes measurements

of the concrete cover the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 5 mm

- where it can be assured that a very accurate measurement device is used for monitoring and non conforming

members are rejected (eg precast elements) the allowance in design for deviation ∆c dev may be reduced

10 mm ge ∆c dev ge 0 mm

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Concrete Workshop

26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 19: [Eng]Advanced Training Concrete Part1 2009.0.1

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19

Analysis models

1_Eurocode

According to EC sect 531

The elements of a structure are classified by consideration of their nature and function as beams columns slabs walls platesarches shells etc Rules are provided for the analysis of the commoner of these elements and of structures consisting ofcombinations of these elements

For buildings the following provisions are applicable

A beam is a member for which the span is not less than 3 times the overall section depth Otherwise it should be considered asa deep beam

A slab is a member for which the minimum panel dimension is not less than 5 times the overall slab thickness

A slab subjected to dominantly uniformly distributed loads may be considered to be one way spanning if either

- it possesses two free (unsupported) and sensibly parallel edges or

- it is the central part of a sensibly rectangular slab supported on four edges with a ratio of the longer to shorter span greater than2

Ribbed or waffle slabs need not be treated as discrete elements for the purposes of analysis provided that the flange or

structural topping and transverse ribs have sufficient torsional stiffness This may be assumed provided that

- the rib spacing does not exceed 1500 mm

- the depth of the rib below the flange does not exceed 4 times its width

- the depth of the flange is at least 110 of the clear distance between ribs or 50 mm

whichever is the greater

- transverse ribs are provided at a clear spacing not exceeding 10 times the overall depth of the slab

The minimum flange thickness of 50 mm may be reduced to 40 mm where permanent blocks are incorporated between the ribs

A column is a member for which the section depth does not exceed 4 times its width and the height is at least 3 times thesection depth Otherwise it should be considered as a wall

2_Scia Engineer

Assignment of analysis model

In Scia Engineer several types of analysis models are available It is up to the user to decide which model should be used forwhich element

For 1D members there is the choice between Beam Beam slab and Column calculation

Each element has a property lsquoTypersquo assigned to it to determine which type of calculation will be used

The Beam calculation is used for the Types lsquoGeneralrsquo lsquoBeam lsquoRafterrsquo lsquoPurlinrsquo lsquoRoof bracingrsquo lsquoWall bracingrsquo lsquoGirtrsquo lsquoTruss chordrsquoand lsquoTruss diagonalrsquo

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 20: [Eng]Advanced Training Concrete Part1 2009.0.1

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20

The Beam slab calculation is used only for the Type lsquoBeam slabrsquo For this type by default no shear reinforcement is added(unless necessary in case of a slab thickness of 200 mm or more as defined in the Concrete Setup for slabs) As diameter forthe longitudinal reinforcement the default diameter for 2D structures ndash and not for beams ndash is taken from the Concrete Setup

The Column calculation is used for the Types lsquoColumnrsquo lsquoGable columnrsquo and lsquoSecondary columnrsquo

Be careful when Member data are added to an element via Concrete menu gt 1D member gt Member data Also there the userhas the choice for the 3 different analysis models by means of the option Beam type

These Member data overwrite both the element properties and the default settings in the Concrete Setup

Difference between Beam and Column analysis model

The most important difference between Beam and Column calculation is the difference in reinforcement area per direction Abeam has an upper reinforcement area that differs from the lower reinforcement area A column always has the samereinforcement configuration for the parallel sides per direction

These configurations are obvious and caused by the difference in dominant internal forces per calculation type For a Beamcalculation the bending moment is dominant while for a Column calculation the axial compression force + bending moments (ifpresent)

So in fact when the axial pressure on a beam is too high the user should choose to calculate the element as a column In theConcrete Setup an option is available to help the user determine whether the Beam calculation type is valid or not Go toConcrete menu gt 1D member gt Setup gt General Calculation gt Tab Beams

Y

Z

Y

Z

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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Concrete Workshop

22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

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To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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21

This option lsquoCheck compression of memberrsquo will check how important the contribution of the axial compression force is

- If the axial compression load Ned lt 01Acfcd warning 60 will appear after reinforcement design

lsquoThe member is not considered to be in compressionrsquo which means the type lsquoBeamrsquo is the right choice

- If the axial compression load Ned gt 01Acfcd warning 61 will appear after reinforcement design

lsquoThe member is considered to be in compressionrsquo which means the beam has to be modelled as type lsquoColumnrsquo

Example

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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30

To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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22

Beam

0_Description of used example

The example that will be used to explain reinforcement calculation in a beam is called beamesa

The beam reinforcement calculation is explained by means of the following two span beam

The length of the total beam is 10 m and it has a dimension of 500x300mm

The inputted loads are

bull BG1 self weight

bull BG2 permanent load

o Line load -27 kNm

o Point load -100 kN at position x = 025

bull BG3 variable load

o Line load -15 kNm

o

Point load -150 kN at postion x = 0

1_Recalculated internal forces

Reinforcement calculation in Scia Engineer is based on recalculated internal forces The pure internal forces calculated by themechanical FEM calculation are transformed according to code regulation into lsquorecalculated internal forcesrsquo to design thereinforcement

These recalculated internal forces can be viewed in the concrete menu of Scia Engineer

Shifting of moment line

The first transformation of internal forces is the shifting of moment line

The Theoretical background on this matter is described below

Sufficient reinforcement should be provided at all sections to resist the envelope of the acting tensile force including the effect ofinclined cracks in webs and flanges

For members with shear reinforcement the additional tensile force ∆Ftd should be calculated according to EN 623 Formembers without shear reinforcement ∆Ftd may be estimated by shifting the moment curve a distance al = d according to EN622 This shift rule may also be used as an alternative for members with shear reinforcement where

al = z (cot θ - cot α )2 (symbols defined in EN 623)

The additional tensile force is illustrated in Figure xx

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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23

In Scia Engineer the user can review the recalculated internal forcesIn the concrete menu it is possible to view the internal forces and recalculated internal forces In the figure below the difference isclearly visible

The shifted moment line is automatically taken into account for recalculated internal forces and by this also for calculation oflongitudinal reinforcement It cannot be found in setup

(The picture is taken from another example on which the difference is shown between My and Myrecalc Note that the value doesnot change since no moment capping at supports is taken into account)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Concrete Workshop

48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 25: [Eng]Advanced Training Concrete Part1 2009.0.1

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25

The reduction of moment by moment capping at supports is illustrated for our example below

t= 02m

FEdsup = 4775 kN

∆MEd = 477502 8 = 1194 kNm

The original moment My at the support was 25416 kNm

The recalculated moment clearly shows the shifting of the moment line

With moment capping at support taken into account the recalculated moment is 24222 kNm

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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Concrete Workshop

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To take the user reinforcement into account the following setting has to be on (default it is on)

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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26

Shear force capping at supports

The theoretical background on shear force capping at supports is described in EN 621 (8)

For members subject to predominantly uniformly distributed loading the design shear force need not to be checked at a distance lessthan d from the face of the support Any shear reinforcement required should continue to the support In addition it should be verifiedthat the shear at the support does not exceed V Rdmax (see also 622 and 623)

In Scia Engineer it is possible to choose between at the face of the support or at a distance d from the face of the support

In the figures below it is clear that the shear force is kept constant over the support

The first figure displays original Vz the second shows the capping at the face the third shows the capping at effective depth from theface

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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27

Other calculation settings

For the calculation of theoretical reinforcement still some other settings can be made

bull Calculate compression reinforcement default is ONDe-activating this option will never calculate compression reinforcement and can thus lead to undesignabilites oruneconomical high amounts of tension reinforcement

bull Normal force to calculation default is ONDe-activating this option will neglect normal force if there is any

bull Check compression of memberIf this is on the value of normal force will be checkedThis check can be interesting for two reasons

If it is a compression force with an absolute value higher than 01sdotAgsdotfcrsquo then this should be calculated as a columnThe beam has to be modelled as type lsquocolumnrsquo

If the absolute value normal force is lower than 01sdotAgsdotfcrsquo then the structure can be assumed as primarily subject tobending In zones primarily subject to bending redistribution of bending moments is allowed This redistribution isnew feature from SE 2010

2 Theoretical reinforcement

Calculation of longitudinal reinforcement As

The longitudinal reinforcement calculation is based on My recalc represented in previous chapter

The only thing left to be set in the concrete setup is the default diameter and material quality

(the default for material quality is B 600C which is a very high performance reinforcement steel this is changed to B 500A forthis example)

If default diameter is set to 16 the following results are obtained

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28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 28: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

28

d lever arm of reinforcement

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 16 2 = 449 mm

(the cover is defined by the environmental class and is 35mm for XC3)

The only internal force working on this beam is Myd Nd and Td are zero

For detailing reinforcement (the reinforcement in the side of the beam) the theoretically required is zero because there is no torsion onthis beam the 2x8 refers to the stirrups

The warnings 67 and 68 are typical warnings that appear when the chosen diameter is too small It means that with this diameter too

many bars are needed resulting in a bar distance which is too small

This gives an indication that it is better to choose a bigger default diameter

If default diameter is set to 20 the following results are obtained

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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29

If you take a close look at these results you can see that also the value for Asreq has changed

This is because the lever arm d has decreased

d = h ndashcover ndash Φstirrup ndash Φlongitudinal beam 2 = 500 ndash 35 -8 ndash 20 2 = 447 mm

As you can see the default diameter has also a slight effect on the amount of reinforcement that is required because of the changedlever arm

We will now input a basic reinforcement and calculate then the additional reinforcement which is needed

As basic reinforcement we will use 2 bars of 20 on the upper and lower side of the beam

Basic reinforcement can be inserted in the beam by use of member data

(Note that concrete data can also be used without setting a number of barsIn that case concrete data are used to change the default diameter for the bar to which these data are assigned It is obvious that themember data have higher priority than the general setup)

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30

To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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To take the user reinforcement into account the following setting has to be on (default it is on)

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The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 31: [Eng]Advanced Training Concrete Part1 2009.0.1

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31

The additional required reinforcement equals the total reinforcement minus the basic user reinforcement

The result is shown below

As you can see graphically we will only need additional reinforcement at the upper face over the support and at the lower face in thefield of the beam

We can input this additional reinforcement by means of practical reinforcement The manual input of practical reinforcement will bedescribed in chapter 3

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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32

Calculation of shear reinforcement Ass

VEd = design shear force from external loading

VRdc = design shear resistance of the member without shear reinforcement

VRds = design value of the shear force which can be sustained by the yielding shear reinforcement

VRdmax = design value of the maximum shear force which can be sustained by the memberlimited by crushing of the compression struts

In general we can have three cases

bull VEd gt VRdmax Concrete strut failure

bull VEd lt VRdc Shear force carried by concrete No shear reinforcement necessary

But minimum shear reinforcement according to detailing provisions

bull VEd gt VRdc and VEd lt VRdmax Shear reinforcement necessary VEd = VRds

The formulas to calculate the shear resistance are given below

Members NOT requiring design shear reinforcement (VEd lt VRdc)

CRdc coefficient derived from tests (recommended 012)

k size factor = 1 + radic(200d) with (d in m)

ρl longitudinal reinforcement ratio ( le002)

fck characteristic concrete compressive strength

bw smallest web width

d effective height of cross section

In SE itrsquos possible to input the following parameters

(note that the green values are according to EN code)

13

1

min 1

(100 )

with a min of

( )

Rd c Rd c l ck cp w

Rd c cp w

V C k f k b d

V v k b d

ρ σ

σ

= +

= +

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 33: [Eng]Advanced Training Concrete Part1 2009.0.1

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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35

Then the configuration of longitudinal reinforcement is shown

The practical reinforcement is shown graphically on the screen

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By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

36

By selecting this reinforcement it is always possible to change this through the property window

Through view parameter settings a 3D representation of the reinforcement can be obtained

To input locally extra practical reinforcement we take back the results for additional reinforcement

On this picture we can precisely define where the extra practical reinforcement needs to be put

To add a new layer of longitudinal reinforcement the following screen will pop up Here can be set on which face extra reinforcementneeds to be added

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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37

For reasons of simplicity we will add 3 bars of 20 that are still required over the whole area where extra reinforcement is required Thiscan of course be done more detailed

The same procedure will be repeated for the upper reinforcement over the support

After adding the extra longitudinal reinforcement we can verify if this is enough through verifying if still additional reinforcement isrequired or not

Also the shear reinforcement needs to be increased in the zones over the support This can be done by increasing the diameter of thestirrups or by decreasing the distance between the stirrupsDifferent stirrup zones can be created

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To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

38

To check if there is enough shear reinforcement a capacity check needs to be performed This will be explained in the next chapter

The total practical reinforcement of the beam is shown below

A zoomed view shows the 3D representation

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Concrete Workshop

44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Concrete Workshop

48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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39

4 Checks

There are some typical checks that can be performed on a beam with practical reinforcement

The following checks are implemented in Scia Engineer

-capacity check checks the interaction of internal forces

-response check checks the maximal strains based on the stressstrain diagram-detailing provisions checks if detailing provisions described in EN chapter 8 and 9 are met

-crack control checks if maximum crack width is not exceed according to EN chapter 73

(-deflections check checks if the long term deflections donrsquot exceed max values (described in chapter CDD))

The capacity and response check should be okay if no additional reinforcement is required

However these checks give interesting information on the efficiency of reinforcement For instance if in a section only 50 ofreinforcement is used then we can conclude that here less reinforcement would have been sufficient

The detailing provisions check and the crack control check are extra checks that are not accounted in the reinforcement design If thesechecks are not okay then the practical reinforcement needs to be changed

We will explain the checks one by one on our exampleYou can start from the esafile beam_practical reinforcementesa

Capacity check

We will start by controlling if there is enough shear force reinforcement by asking the report for Vzu

As expected the unity check is higher than one so this is not okay

We will increase shear force reinforcement also in the middle zones to solve this problem

This is done in the new f ile beam_practical reinforcement2esa

It is also possible to do a single check in a specific section of the beam

This gives very detailed information on the interaction diagram as shown below

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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Concrete Workshop

58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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41

Response check

The response check is related to the stress strain diagram and checks if maximal strains arenrsquot exceeded As mentioned above thischeck is satisfied if no additional reinforcement was required

Below the single check over the support is shown

It is clear from this picture that the upper side is in tension and that the concrete does not work in tension All tension has to be taken bythe upper reinforcement bars

Below the stressstrain diagrams are shown for the lower and upper fibre of concrete and for the upper reinforcement bar

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 43: [Eng]Advanced Training Concrete Part1 2009.0.1

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43

Detailing provisions check

The check of detailing provisions checks the detailing provisions activated in the concrete setup Since the EN requires to check thesedetailing provisions it is adviced to activate them all Note that default they are all activated

The check of detailing provisions is shown below

The problem in this example is that the surface to surface spacing of longitudinal reinforcement is less than the minimum

The minimum bar spacing is the bigger of

bull k1 bar diameter (k1 = 1 in default setup (EN 82 (2))bull dg + k2 (k2 = 5mm in default setup (EN 82 (2))

(dg is the stone diameter and can be set in that material properties)bull 20 mm (20 mm (EN 82 (2))

A possible solution would be to replace the 5 bars of 20 mm by a smaller amount of bigger bars

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Concrete Workshop

44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Concrete Workshop

48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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44

Crack control check

The unity check for crack control in Scia Engineer is the bigger of three checks

- crack width (w gt wlim)

- minimum reinforcement area (Asprov gt Asmin)

- maximum bar diameter and distances (itrsquos sufficient that either the distances or the diameters satisfy)

The formula for crack width can be found in EN 734

The allowable crack width can be set in the setup

For environmental class XC3 wlim equals 04mm

The formula for minimum reinforcement area can be found in EN 732

Asminσs = kc k fcteff Act

max( )k r sm cmw s ε ε = minus

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 46: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

46

5 Automatic member reinforcement design

In chapter two of the chapter beam calculation the theoretical design of reinforcement was explained In chapter three practicalreinforcement was inserted manually based on the amount of required reinforcement In chapter four a response check andcapacity check was performed

This procedure is collected in the option lsquoAutomatic reinforcement designrsquo

Automatic reinforcement design takes into account

-capacity check

-response check

-detailing provisions minimum and maximum percentage and maximum bar distances

The method of AMRD is explained by means of the same example explained in 0_description of used example

Open this example beamesa

First of all we have a look at the theoretical design Itrsquos always recommended to do this before you perform an AMRD On thatway you have an idea of the amount of reinforcement and the possible minimum diameter

For example a basic diameter of 10 mm and quality B 600C is taken in the setup of concrete The following output is obtained

Itrsquos obvious that this diameter cannot be used for a design because of the bar distances So we increase the diameter in thesetup to 16 mm

Also in this case the bar distance is too small However for an automatic design one layer can contain a mix of diameters Sowe keep the diameter of 16 mm as minimum

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Concrete Workshop

48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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47

Now we can do an automatic reinforcement design There are 3 manners to do this

bull By means of the setup

bull By means of the member data

bull By means of a reinforcement template

The 3 options will be explained

AMRD by means of the setup

Project AMRD01esa

First of all the minimum diameter has to be determined in the setup This was done in the previous step

After this some settings of the AMRD can be adapted in the setup of concrete

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Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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48

Explanation of the AMRD-parameters

General

Maximum exploitation of cross-section

Specifies the maximal utilisation of the cross-section in the automatically reinforced beam

The value may be between 1 and 100

Longitudinal reinforcement

Minimal length of bars

Defines the minimal length of bars automatically inserted into the reinforced beam The algorithm tries to shorten thereinforcement bars if possible so that they do not extent along the whole length of the beam The shortened bar cannot beshorter than the value of this parameter

Check minnumber of longitudinal bars above supports

If ON the number of reinforcement bars above supports is checked and compared to the values specified below

Minimum number of longitudinal bars above supports

Defines the minimal required amount of reinforcement bars above supports

Try to reduce length of bars

If OFF the program uses only bars that extent along the whole length of the beam

If ON some bars may be shortened if the unity check is satisfied without them

Minimal number of bars in reinforcement layer

Imagine a simply supported beam There must be 6 bars in the middle of the span Only 5 bars are required in a section that iscloser to the support And only 4 bars are necessary in another section that is still closer to the support And so on So in

general you could shorten the bars one by one This may be sometimes impractical as it would lead to a large number ofdifferent bars

The value in this parameter defines the minimal number of bars that may be shortened at the same time The default value is 2It means that in our example you would have 6 bars in the middle there still will be 6 bars in the section where 5 is sufficientand only farther towards the support the number will be reduced to 4 bars And so on

Maximal number of bigger diameters than the default

Defines how many different (bigger) diameters of the reinforcement can be used for the optimisation Let us assume that thedefault diameter specified in the Design default tab is 10mm

If this parameter is set to 2 the program can use diameters 10 12 (ie +1 item in the manufacturing programme) and 14 (ie+2item in the manufacturing programme) for the design

Do not use Neighbouring bars

Some standards recommend that neighbouring profiles from the manufacturing programme should not be used in one beam (inorder to avoid unintentional interchange of the profiles)

Let us assume that the default diameter specified in the Design default tab is 10mm Further assume that Maximal number ofbigger diameters than the default is set to 2

If this option is ON the following bars can be inserted into the beam (i) either 10mm (ii) or 12mm (iii) or 14mm (iv) or 10mmand 14mm can be combined together 10mm and 12mm are

not permitted to be combined in one beam

Stirrups

Minimal centre-to-centre distance for stirrups

Specifies the minimal distance between stirrups measured from the centre of a bar to the centre of an adjacent bar

Minimum reduction length

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 49: [Eng]Advanced Training Concrete Part1 2009.0.1

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49

Defines the minimum reduction length It may be defined by means of length or number of stirrups in the part See the next twoparameters

Minimal length of one stirrup part

Defines the length of one part of the beam where stirrups are distributed uniformly This parameter ensures than a situation thedistance between two adjacent stirrups is different for every two adjacent stirrups

Minimal number of stirrups in one stirrup partAnalogous to the parameter above

Step for reduction

Defines the step for the reduction of the distance between two adjacent stirrups This insures that the distance between stirrupsis always a rounded number ndash eg 200mm then 250mm then 300mm etc (and not eg 200 246mm 298mmetc)

Symmetrical part of stirrups

This parameter may enforce that the stirrup part are symmetrical along the length of the beam

To see the influence of the diameter we change the maximal number of bigger diameters than the default diameter into 0

Now we can perform a Reinforcement design

Go to Automatic member reinforcement design gt Reinforcement design

And select combination ULS

After refreshing the following result is obtained

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Concrete Workshop

50

Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Concrete Workshop

52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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Concrete Workshop

58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Scia Engineer canrsquot found a solution at some locations This was expected because we stated that only the diameter 16 couldbe used The bar distances will be too small

So we go back to the concrete setup and change the Maximal number of bigger diameters than the default diameter into 2 So16 20 and 25 mm can be used

The previous reinforcement is deleted now and after refreshing the amount of reinforcement is

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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51

AMRD by means of the conrete data

Project AMRD02esa

In the first step Member data are input on the beam So go to Member data in the concrete menu and select the beam

Next some basic reinforcement is chosen namely 2 bars of diameter 20mm at the upper and lower side

Remark it not obligated to insert a number of bars itrsquos also possible to insert only a basic diameter

Once this is done the member data under Automatic reinforcement design can be input

Select Automatic member reinforcement design gt Member data

The question arises

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Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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52

Confirm this by clicking on Yes

Finally the dialog box for the stirrup shape manager opens

In the parameters the option lsquoBy member datarsquo has to be selected In that way the basic reinforcement of the member data willbe used

Click OK to insert the member data

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53

This results in the reinforcement configuration

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AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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53

This results in the reinforcement configuration

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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54

AMRD by means of a reinforcement template

Project AMRD03esa

A last option to do an AMRD design is according to a reinforcement template This can be determined in the AMRD data

Open AMRD02esa and delete the previous calculated reinforcement Select the label AMRD1 and click on the button behind

Reinforcement template

Here the option Parameters is switched to lsquoBy templatersquo

In that case the selected template LR_B_R1 is used as basic reinforcement Click on the button lsquoEditrsquo to see the reinforcementparameters

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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55

Create the following configuration

Upper 2 bars of 20 mm

Lower 2 bars of 25 mm

Middle leftright 1 bar of 16 mm

Select the tab Automatic design

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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56

Note that this option is checked for the upper and lower bars The bars in the middle are not taken into account for the automaticdesign

This means that the upper and lower bars will be used to vary during the design process

For example the first configuration that will be verified is the configuration of the template Suppose that this gives a capacitycheck higher than 1 So new bars are added or diameters are changed (only 2 diameter higher) to satisfy the check

The two flank bars however are not taken into account in the automatic reinforcement design This means that they are includedfor the checks but their diameter or number will not vary during the process

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Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 57: [Eng]Advanced Training Concrete Part1 2009.0.1

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57

Column Design

Calculation TypesWhen taking a closer look at the column calculation 2 different approaches can be distinguished

- For the lsquoAxial compression onlyrsquo and lsquoUni-axial bendingrsquo calculation Scia Engineer uses the same computing heart as forbeams

- For lsquoBi-axial bendingrsquo calculations Scia Engineer uses a combination of the computing heart for beams and the so-calledinteraction formulas

Furthermore the uni-axial bending calculation always has as result a 1-directional reinforcement configuration with the samenumber of reinforcement bars at parallel sides The bi-axial bending calculation has as result a 2-directional reinforcementconfiguration The number of bars may differ per direction but is always the same for parallel sides

The uni-axial bending calculation is a relatively simple calculation type while the bi-axial bending calculation requires an iterativeprocess Keep this in mind as the reason why the uni-axial bending calculation will go a lot faster

Axial compression only

No reinforcement required (NEd lt NRd)

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results (According to the Eurocode always a minimumreinforcement percentage has to be added)

Loads

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BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 58: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

58

BG1 Permanent load gt F = 1100 kN

BG2 Variable load gt F = 1000 kN

This means the column is loaded with a single compression force

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 1100 + 150 1000 = 2985 kN

Bar diameter

The bar diameter is taken from the Concrete Setup gt Design defaults gt Tab Columns or from Member data if applied (Memberdata always overwrite the Concrete Setup data for the specific member they are assinged to)

By default the diameter for the main column reinforcement is put to 20 mm Based on this diameter and the exposure class (bydefault XC3) the concrete cover is calculated This information is necessary to be able to calculate the lever arm of thereinforcement bars

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action button [Refresh] The value 0appears on the screen followed by warning 77

Select now the option lsquoPrint explanation of errors and warningsrsquo in the Properties menu and click the action [Preview] Thefollowing screen will appear

No theoretical reinforcement is required Remark this result is obtained only because all of the detailing provisions aredeselected in the Concrete Setup

Check of reinforcement

NRd = fcd middot α middot Ac

= 30 middot 085 middot 3502 1000 = 3124 kN

Since NRd = 3124 kN gt Nd = 2985 kN indeed no theoretical reinforcement is required

Reinforcement required (NEd gt NRd)

For this example the same configuration as above is used only the permanent point load is increased to 2000 kN

Loads

BG1 Permanent load gt F = 2000 kN

BG2 Variable load gt F = 1000 kN

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 2000 + 150 1000 = 4200 kN

Results

Remark that Scia Engineer shows on the screen the reinforcement per direction The total reinforcement area is in fact 750 +750 = 1500 mm

2

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Concrete Workshop

64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 59: [Eng]Advanced Training Concrete Part1 2009.0.1

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59

When going to Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottom ofthe Properties menu There the proposed configuration can be found

Explanation of the number of reinforcement bars

In the previous example the configuration of required reinforcement bars was noted as 8(66) which stands for ldquo6 bars in the ydirection (3 bars per side y) 6 bars in the z direction (3 bars per side z)rdquo This is a simple representation of the barconfiguration so the user can easily understand how the bars should be inputted

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 60: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

60

Uni-axial bending

For uni-axial bending 2 types of calculation are supported the (sum) and the (max) calculation

Uni-axial bending calculation (sum)

Principle

The reinforcement is designed separately around both axes and the final area of reinforcement is the sum of reinforcement forboth directions

Asy is designed for forces NEd and MEdy

Asz is designed for forces NEd and MEdz

As = Asy+Asz

This calculation often gives uneconomic solutions for the reinforcement This is the reason another calculation type has beenimplemented uni-axial bending calculation (max) which may be used in most situations See paragraph Calculation methodsOverview ndash Automatic design to understand how is determined which calculation may be used

Uni-axial bending calculation (max)

Principle

The reinforcement is designed only around the axis with the bigger bending moment

If MEdy gt MEdz As = Asy is designed for forces NEd and MEdy

If MEdz gt MEdy As = Asz is designed for forces NEd and MEdz

Example open the example Axial force ndash uni ax bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 mConcrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item Detailing provisions not taken into account to view the pure results

Loads

BG1 Permanent load gt F = 500 kN My = 100 kNm

BG2 Variable load gt F = 1000 kN My = 100 kNm

Combination according to the Eurocode

ULS Combination = 135 BG1 + 150 BG2

Design normal force Nd = 135 500 + 150 1000 = 2175 kN

Design moment Myd = 135 100 + 150 100 = 285 kNm

F

M

L

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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Concrete Workshop

62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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61

Results

Go to Concrete menu gt Member design - Design ask the value for As and click the action buttons [Refresh] and [Preview] Thenumerical results of the calculation are as follows

Remark the calculation type Um (Uni-axial bending (max))

Remark that ratio yz is 1000 all of the reinforcement works in 1 direction

When going to the Concrete menu gt Member design - Design the user has the choice for the action Single Check at the bottomof the Properties menu There the proposed configuration can be found

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 62: [Eng]Advanced Training Concrete Part1 2009.0.1

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62

Bi-axial bending

EC Theory

To decide if a bi-axial bending calculation is required or not the following conditions should be checked according to EC sect589(3)

If the slenderness ratios satisfy the following two conditions

(EC expression 538a )

If the relative eccentricities e y h and e z b satisfy one of the following conditions

(EC expression 538b )

where

b h are the width and depth of the section

b eq = i y radic 983089983090 and h eq = izradic 983089983090 for an equivalent rectangular section

λ y λ z are the slenderness ratios l 0 i with respect to y - and z -axis respectively

i y i z are the radii of gyration with respect to y - and z -axis respectively

e z = M Edy N Ed eccentricity along z -axis

e y = M Edz N Ed eccentricity along y -axis

M Edy is the design moment about y-axis including second order moment (if required)

M Edz is the design moment about z-axis including second order moment (if required)

N Ed is the design value of axial load in the respective load combination

If the conditions of expression (538a ) and (538b ) are NOT fulfilled bi-axial bending should be taken into account

F

M

L

Mz

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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63

According to EC sect 589(4) in the absence of an accurate cross-section design for bi-axial bending the following simplifiedcriterion may be used

(EC expression 539 )

where

M Edzy is the design moment around the respective axis including a 2nd order moment (if required)

M Rdzy is the moment resistance in the respective direction

a is the exponent for circular and elliptical cross sections a = 2

for rectangular cross sections

with linear interpolation for intermediate values

N Ed is the design value of axial force

N Rd = Acf cd + Asf yd the design axial resistance of the section

where

Ac is the gross area of the concrete sectionAs is the area of longitudinal reinforcement

The criterion described by EC condition 539 ndash which is known as the interaction formula ndash is also implemented in Scia Engineeras basis for the bi-axial bending calculation Only the notation lsquoarsquo for the exponent (= safety factor) of the interaction formula hasbeen replaced by an lsquoxrsquo See Concrete menu gt Setup gt General Calculation gt Tab Columns

By default the safety factor is calculated automatically by Scia Engineer according to the requirements of the Eurocodementioned in the previous paragraph

Also the notation for M Rdy and M Rdz has been replaced by Muy and Muz in Scia Engineer These are the ultimate moments themoments that can be carried by the concrete + the present reinforcement bars

Iteration process for bi-axial bending calculation

The increment routine for the number of bars as implemented in Scia Engineer is as follows

Start situation

One reinforcement bar in each corner

The diameter of the reinforcement bars is taken from the Concrete Setup or from Member data

Check of interaction formula

Scia Engineer determines the values for Myu and Mzu for the present reinforcement layout and calculates the interactionformula

If the value is less than 1 the calculation is stopped

Increment step 1

For the weakest direction 1 bar per side is added

Check of interaction formulaScia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped

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Concrete Workshop

64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

64

Calculation of moment ratios

For each one of the design moments (Myd and Mzd) Scia Engineer determines the normal stress in the exterior fiber by

dividing the design moment by the resistance moment W for that direction This means that σy = Myd Wy and σz = Mzd Wz

Based on these σs the ratio of the moments can be determined per direction

ry = σy (σz + σy) and rz = σz (σz + σy)

Increment step 2 to hellip

According to the values for ry and rz the reinforcement is now increased per direction

- For the strongest direction 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1r The value ofn1r is rounded off to integer even values

Check of interaction formula ndash after each increment step

Scia Engineer determines the new values for Myu and Mzu and recalculates the interaction formula

If the value is less than 1 the calculation is stopped If this is not the case increment step 2 is repeated until the interactioncheck does satisfy

Iteration process ndash Example

The iteration process used by Scia Engineer can be simulated by means of an example where each time the values for the loadsare increased Remark that the ratio between the design moments stays the same while the values are increased

Example open the example Bi axial bendingesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C2530

Elastic resistance moments Wy = 16 middot 3503 = 715middot10

6 [mm

3] = Wz

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

Item General Calculation gt Tab Columns lsquoOptimize the number of bars in cross-section for bi-axial calculationrsquo is deselected

Item Detailing provisions All of the provisions are deselected (to have a look at the pure results)

Loads

Final load configuration Nd = 105000 kN Myd = 12250 kNm Mzd = 20625 kNm

Start situation

The start situation is always one reinforcement bar per corner The bar diameter is taken from the Concrete Setup or fromMember data (if applied)

Simulation Column B1

Nd = 105000 kN

Myd = 5123 kNmMzd = 8625 kNm

Reinforcement configuration (44) ndash This configuration can be found when going to Concrete menu gt Member design -Design and choose the action Single Check for column B1 at the bottom of the Properties menu

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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65

Check of interaction formula

Myu = Mzu = 1484 kNm

These values can be found when going to Concrete menu gt Member design - Design and choose the action Single Check forcolumn B1 at the bottom of the Properties menu On the tabs lsquoVertical section Myrsquo (where Mdz = 0 kNm) amp lsquoVertical section Mzrsquo(where Mdy = 0 kNm) these specific sections from the interaction diagram are shown and the ultimate values Myu and Mzu areindicated to it

Interaction formula (122501484)14

+ (206251484)14

= 235 gt 1

Increment step 1

For the weakest direction z 1 bar per side is added

Simulation Column B2

Nd = 10500 kN

Myd = 5717 kNm

Mzd = 9625 kNm

Reinforcement configuration (46)

Check of interaction formula

Myu = 1503 kNm Mzu = 1829 kNm

Interaction formula (122501503)14

+ (206251829)14

= 193 gt 1

Calculation of moment ratios

ry = 12250 32875 = 037 and rz = 20625 32875 = 063

The values for Mdy and Mdz are taken from the final load configuration

Increment step 2 ndash 3 ndash 4

- For the strongest direction y 1 bar per side is added

- For the weakest direction the new number of bars in the lsquostrongestrsquo direction (n) is taken and multiplied by 1rz (= 1063 =159) The value of n1rz is rounded off to integer even values

Simulation Column B3

Nd = 105000 kN

Myd = 8686 kNm

Mzd = 14625 kNm

y 4+2 = 6 bars

z 6159 = 954 ~ 10 bars

Reinforcement configuration (610)

8122019 [Eng]Advanced Training Concrete Part1 200901

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

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The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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67

For the final load configuration represented by column B5 the interaction check is 81 lt 100

As the requirement for the interaction check is met the iteration process is stopped and the solution for the reinforcementconfiguration is (1016)

Optimization

There might be a more optimal solution with an interaction check even closer to 100 A specific option has been implementedto make Scia Engineer look for such a solution

Go to Concrete menu gt Setup gt General Calculation gt Tab Columns and activate the option lsquoOptimize the number of bars incross-section for bi-axial calculationrsquo

Return now to Member design - Design and open the Preview again

We can conclude that indeed a more optimal solution is found where the reinforcement configuration is only (1014) instead of(1016) and the interaction check is now 89 instead of 81

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 68: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

68

Calculation methods Overview ndash Automatic design

Concrete Setup gt General Calculation gt Tab Column

After selecting the option lsquoAdvanced settingrsquo the option Calculation Method becomes available

The user can enforce now 1 of the 3 calculation methods if desired By default the option is put to Automatic determination Inthat case Scia Engineer automatically determines which type of calculation fits best for each column in the structure

- First is checked if the conditions according to EC sect 589(3) are fulfilled

- Secondly a ratio check of the bending moments in the different directions is carried out The check value of 10 forms (bydefault) the boundary between uni-axial and bi-axial bending calculation

The Automatic determination in Scia Engineer can be summarized in a flow chart as follows

Circular columnsScia Engineer is able to calculate reinforcement not only for rectangular but also for circular columns

The calculation method for circular columns is the most simple one because the required number of reinforcement bars isspread equally along the face of the column

Example

Example open the example Circular columnesa

Geometry

Column cross-section CIRC diameter 400mm

Height 45 m

Concrete grade C4555

Concrete Setup

Item General Calculation gt Tab Columns lsquoBuckling datarsquo are not taken into account (only 1st order moments are considered)

8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7579

75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 6979

8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7279

Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7379

73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 70: [Eng]Advanced Training Concrete Part1 2009.0.1

8122019 [Eng]Advanced Training Concrete Part1 200901

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8122019 [Eng]Advanced Training Concrete Part1 200901

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7279

Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7379

73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7479

Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7579

75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7679

Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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71

In cases with biaxial bending the slenderness criterion may be checked separately for each direction Depending on theoutcome of this check second order effects (a) may be ignored in both directions (b) should be taken into account in onedirection or (c) should be taken into account in both directions

Taking geometric imperfections into account

The effect of geometric imperfections always has to be taken into account both in a 1st and 2

nd order calculation For isolated

members there are 2 alternative ways to do so according to EC sect 52 (7)

a) As an eccentricity e i given by

e i = θi l0 2 (EC formula 52 )

where l0 is the effective length

For walls and isolated columns in braced systems e i = l 0 400 may always be used as a simplification corresponding to αh = 1

b) As a transverse force H i in the position that gives the maximum moment

- for unbraced members

H i = θi N (EC formula 53a )

- for braced members

H i = 2 θi N (EC formula 53b )where N is the axial load

According to EC sect 589 (2) imperfections need to be taken into account only in the direction where they will have the mostunfavourable effect

Taking 2nd order effects into account

Several methods are described by the Eurocode to take into account 2nd

order effects The one implemented in Scia Engineer isthe method based on the nominal curvature (EC sect 588 ) In fact this is an approximation of a genuine 2

nd order calculation only

1st order moments are calculated and then increased by 2

nd order moments which are calculated based on the 1

st order internal

forces

The explanation is as follows

This method is primarily suitable for isolated members with constant normal force and a defined effective length l 0 The methodgives a nominal 2

nd order moment based on a deflection which in turn is based on the effective length and an estimated

maximum curvature

The design moment is

M Ed = M 0Ed+ M 2 (EC formula 531)

where

M 0Ed is the 1st order moment including the effect of imperfections see also 5882

M 2 is the nominal 2nd order moment see 5882

The maximum value of M Ed is given by the distributions of M 0Ed and M 2 the latter may be taken as parabolic or sinusoidal overthe effective length

Differing first order end moments M 01 and M 02 may be replaced by an equivalent first order end moment M 0e

M 0e = 06 M 02 + 04 M 01 + 04 M 02 (EC formula 532 )

M 01 and M 02 should have the same sign if they give tension on the same side otherwise opposite signs Furthermore |M 02|ge |M 01|

The nominal second order moment M 2 in expression (531) is

M 2 = N Ede 2 (EC formula 533 )

where

N Ed is the design value of axial force

e 2 is the deflection = (1r ) c

1r is the curvature

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 72: [Eng]Advanced Training Concrete Part1 2009.0.1

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Concrete Workshop

72

l o is the effective length

c is a factor depending on the curvature distribution

For constant cross section c = 10 (asympπ2) is normally used If the first order moment is constant a lower value should be

considered (8 is a lower limit corresponding to constant total moment)

The curvature 1r can be calculated as follows for members with constant symmetrical cross sections (incl reinforcement)

1r = K r K ϕ 1r 0 (EC formula 534 )

where

K r is a correction factor depending on axial load

K ϕ is a factor for taking account of creep

1r 0 = εyd (045 d )

εyd = f yd E s

d is the effective depth

Overview

All of this can be summarized as follows

(1) Check if λ lt λlim(2) If 2

nd order effects have to be taken into account Check if the method based on the nominal curvature is valid so a nominal

2nd

order calculation can be carried out If not a real non-linear 2nd

order calculation has to be performed

8122019 [Eng]Advanced Training Concrete Part1 200901

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7679

Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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73

Scia Engineer

Check if λ λλ λ lt λ λλ λ lim

This values for λ and λlim and the corresponding check can be found in the Concrete menu gt Concrete slenderness

If λ gtλlim 2nd

order effects have to be taken into account

Option lsquoBuckling datarsquo

In the Conrete menu gt Setup gt General Calculation gt Tab columns the option lsquoBuckling datarsquo can be found By default thisoption is activated

It is important to know that- When this option is not activated only the 1

st order bending moments are taken into account

- When this option is activated also the moments caused by geometrical imperfections and the nominal 2nd

order moments aretaken into account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0)

e1 = Md Nd

(Where Md Nd are the values from 1st order calculation)

Note that if no second order moment is required according to art 5831 only the moment caused by geometrical imperfectionsis taken into account and not the second order moment

Effective length

The effective length (=buckling length) is calculated by default by Scia Engineer Attention this is only valid for simple structures

In Concrete menu gt Setup gt Design defaults can be found that for buckling around the local y axis (Y-Y) aacutend for for bucklingaround the local z axis (Z-Z) the structure is by default considered as lsquoswayrsquo

Off course the user can assign specific buckling data to each member separately To do so select a member and click in theProperties menu on the [] button behind lsquoBuckling and relative lengthsrsquo Here you can choose to input your own buckling factor(beta) or length (l)

The effective length based on these buckling data is required to calculate e2 and the corresponding moment M2

Recalculated internal forces

In the Concrete menu gt Internal forces the following results can be asked for

- The values for Mx My Mz which are the 1st order design moments

- The values for Mxrecalc Myrecalc Mzrecalc which are the recalculated design moments where the moments caused bygeometrical imperfections and the nominal 2

nd order moments are taken into account (M Ed = M 0Ed+ M 2)

Reinforcement design

In the Concrete menu gt Member design - Design the values for Asreq are calculated based on the recalculated design valuesof the internal forces (Myrecalc and Mzrecalc)

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

74

Example

Example open the example 2nd orderesa

Geometry

Column cross-section RECT 350x350mmsup2

Height 45 m

Concrete grade C4555

Concrete Setup

All of the default values are kept

Loads

Load configuration Nd = 40500 kN Myd = 4050 kNm Mzd = 0 kNm

Buckling data

Note that the option buckling data is by default activated This means that for reinforcement design automatically the geometricalimperfections are taken into account Since geometrical imperfections are taken into account no extra buckling check isrequired The calculation of geometrical imperfections is based on the buckling length l0

To view or edit the basic settings for calculation of buckling length l0 the user can access the buckling properties of a memberthrough the properties gtBuckling and relative lengths

Slenderness criterion

Check if second order calculation is required following art 5831

Since λ is greater than λlim second order calculation will be required

Note that the program automatically takes into account a second order moment if required So this check is just extra informationfor the user

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7579

75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7679

Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 75: [Eng]Advanced Training Concrete Part1 2009.0.1

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75

Internal forces

-basic

-recalculated internal forces taking into account geometrical and second order imperfection (both are automatically calculatedbased on l0 if of course option buckling data is not manually de-activated)

Results

The results for the reinforcement design are shown below

Note that Biaxial bending is the calculation type even though no Mz is applied to the column

This is because of the second order moment that causes a moment Mz to be taken into account for design

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7679

Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

8122019 [Eng]Advanced Training Concrete Part1 200901

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7879

Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

76

Concrete Setup Overview

Concrete menu gt 1D member gt Setup gt General Calculation gt Tab Columns

Basic Settings

Corner design only

This is a special type of calculation where the reinforcement is designed only in the corners of the cross-section with an internalangle of 90deg It is an iterative calculation where the number of bars stays the same but the diameter or area of reinforcement isincreased until the configuration satisfies the ULS checks

The way of increasing the diameter depends on the setting of the option lsquoDesign reinforcement by using real area delta arearsquo(discussed further in this paragraph)

The position of the corner bars is calculated in both cases from parameters (such as concrete cover) defined in the ConcreteSetup or in the Member data and the position is not changed during the iteration calculation

Only the basic concrete sections are supported for this calculation (see Libraries gt Cross-sections gt group Concreterectangular I - T- L-sections) The number of bars depends on the shape of the cross-section

Basic settin s

Advanced settin s

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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77

Determine governing cross-section beforehand

When this option is on the design of the reinforcement is only carried out in the foot and head of the column When this option isoff the design is carried out in all intermediate sections as well which may be time consuming and brings no profit in terms ofaccuracy

The subsequent check of the designed reinforcement is in both cases performed in all sections

Remark the option lsquoDetermine governing cross-section beforehandrsquo is not taken into account in the action Single Check

Buckling data

When this option is off only the 1st order bending moments are taken into account

When this option is on also the moments caused by geometrical imperfections and the nominal 2nd

order moments are takeninto account This means the eccentricities ei and e2 have to be calculated supplementarily and in this way the problem ofbuckling is also taken care of (e2 depends of the buckling length l0) In fact it is an approximation (described by the Eurocode) ofa genuine 2

nd order calculation only 1

st order moments are calculated and then increased by 2

nd order moments which are

calculated based on the 1st order moments

Optimize the number of bars in cross-section for bi-axial calculation

If this option is on the number of bars in the cross-section is optimised to achieve the minimum number of bars with the cross-

section still passing the ULS checks

This option only has influence on the reinforcement of members where a bi-axial calculation is performed In fact Scia Engineerlooks for the solution where the value for the interaction formula is as close to 1 as possible

Advanced Settings

These are only available when the option lsquoAdvanced settingrsquo is selected

Calculation method

The user has the choice between 3 calculation methods Uni-axial bending calculation (sum) or (max) and Bi-axial bendingcalculation

By default the option lsquoAutomatic determinationrsquo is selected Scia Engineer follows a certain flow chart then to determine whichcalculation is best suited (See paragraph Bending ndash Overview for the flow chart)

Design reinforcement by using real area delta area

The choice made here is only taken into account for bi-axial bending calculation and corner design only which are both iterativecalculations It defines the way in which the required reinforcement area is increased in each iteration step

Real area of reinforcement bar

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the real sectional area of an individual reinforcement bar Thismeans that the value for Asreq is always a multiple of the area of the used reinforcement bar

8122019 [Eng]Advanced Training Concrete Part1 200901

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

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Concrete Workshop

78

For corner design only

The diameter of the corner bars is increased in each iteration step according to a list of basic diameters which is for theEurocode 5-6-8-10-12-14-16-20-25-28-32-40 mm As initial value for the bar diameter the default value from the ConcreteSetup or from the Member data (if applied) is taken If the last diameter from the list doesnrsquot satisfy yet the calculation is endedwith error 508

Delta area of reinforcement

For bi-axial bending calculation

If this option is on the value for Asreq is calculated based on the user defined delta area This means that the value for Asreq isalways a multiple of the value inputted by the user

(In this case a value for delta area of 20mmsup2 has been inputted)

For corner design only

The value for delta area represents the increasing area per reinforcement bar in each iteration step The lsquorealrsquo diameter ofreinforcement bars dsi after each iteration step i is calculated according to the formula below and is rounded up to an integer

Bi-axial bending ndash Safety factor

The value for the safety factor x used in the interaction formula can be determined automatically or by user input

When the option lsquoAutomaticrsquo is chosen Scia Engineer calculates the factor x by means of the following rules from the Eurocode

x = 2 for circular and elliptical cross-sections

x = the value lsquoarsquo according to the following table for rectangular cross-sections (with linear interpolation for intermediate values)

Bi-axial bending ndash Ratio yz

Automatic

Scia Engineer calculates the ratio yz automatically after the design has been done

Manual

The user can impose a ratio yz so the reinforcement configuration will be adapted to meet this requirement

From user reinforcement

The ratio of the reinforcement in y and z direction is calculated from existing user reinforcement

( )

ratio

( )

y

y z

z

y z

n

n n y

n zn n

+=

+

where ny = number of bars in the y direction nz = number of bars in the z direction

If no user reinforcement is defined then the ratio yz = Automatic

If the user reinforcement is unsymmetrical about y or z axis then error 879 will appear ldquoThe calculation is not supportedbecause of unsymmetrical user reinforcementrdquo

Bi-axial bending ndash Limit stress ratio yz

This is the limit value for the ratio yz of additional (or required) reinforcement for a bi-axial bending calculation

π

i Adsi

sdot∆sdot=

4

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)

Page 79: [Eng]Advanced Training Concrete Part1 2009.0.1

8122019 [Eng]Advanced Training Concrete Part1 200901

httpslidepdfcomreaderfullengadvanced-training-concrete-part1-200901 7979

The default value for (ratio yz)lim is 4 If ratio yz gt (ratio yz)lim or ratio yz lt 1(ratio yz)lim then warning 245 will appear ldquoAnunusual design situation is encountered the stress ratio yz exceeds the preset limit or the required reinforcement is hardlyacceptablerdquo This is due to too many bars in 1 direction and the solution is to

- use a different Calculation Method

- use a different Ratio yz

- switch on the option lsquoOptimize the number of barsrsquo (best solution)

User estimate of reinforcement ratio for design of reinforcementThis estimated value for the reinforcement ratio is used to calculate the nominal curvature 1r according to EC sect 5883 wherethe value for As has to be filled in The value for As is then taken as the lsquoreinforcement ratio Acrsquo

Since the nominal curvature is only needed for the calculation of second order effects this ratio is only calculated for memberswith ldquoBuckling datardquo on

The default value for the ratio is 2 If the ldquopercentage of additional (required) reinforcement is less than 80 of user estimateratio then Scia Engineer gives warning 270 If the ldquopercentage of additional (required) reinforcement is greater than 120 ofuser estimate ratiordquo then Scia Engineer gives warning 271

Take into account eccentricity according to chapter 614

If this option is on the first order eccentricity including imperfections (e0) in both directions has to be the maximum of (h30 20mm) where h is the depth of the section

This option is implemented according to the EC sect 61(4)