simple construction

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Columns in Simple Construction(NCCI: Determination of moments on columns in simple construction &

NCCI: Verification of columns in simple construction)



Columns in Simple Construction

• Connections are assumed not to develop significant moments

adversely affecting either the members or the structure as a

whole.

• The beams may be designed as simply supported.

• The columns are designed to carry axial loads as well as

nominal moments from the reaction shear of the beam,

applied at the appropriate eccentricity.

• Columns must be fully continuous.

• It is assumed that sidesway due to horizontal loading is

prevented by inserting bracing or by utilising shear walls, lift

or staircase closures, acting together with shear resistance of the floor slab.

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Joints in Simple Construction

100 mm

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Simple Construction

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Simple Braced

Frame

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Simple Construction• Connections are assumed not to develop significant

moments adversely affecting either the members or the

structure as a whole.

• The beams to be designed as simply supported.

• The columns are designed to carry axial loads as well as

nominal moments from the reaction shear of the beam,applied at the appropriate eccentricity.

• Columns must be fully continuous.

• It is assumed that sidesway due to horizontal loading is

prevented by inserting bracing or by utilising shear walls,

lift or staircase closures, acting together with shear

resistance of the floor slab.

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No need to consider pattern loading as

shown below

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8

h/2

h

R

100 mm

Moment = R x (h/2 + 100 mm)

h is the depth of the column

Beam connected toColumn Flange

t w/2

t w

100 mm

Moment = R x (t w

/2 + 100 mm)

t w is the thickness of the column web

R

Beam connected toColumn Web

Eccentricity of Loading



R1

R3

R2

My=R 2(h/2+100)Mz=R 1(tw /2+100) –

R 3(tw /2+100)y

y

zz

h = depth of column

tw = web

thickness



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The applied moment is divided between the

column lengths above and below in

proportion to the column stiffness ( EI / L).eg. Moment M 3 is divided into M 3-4 and M 3-2 in

proportion to ( EI )34/l34 and ( EI )23/l23 respectively.

If the stiffness ratio

1.5, the moment maybe divided equally.

The moments have no effect at levels

above and below.eg. Moment M 3 is distributed to M 3-4 and M 3-2

only and will have no effect on M 4-3 and M 2-3.

M 3 M 3-2

M 3-4

M 4 M 4-3

M 4-5

M 2 M 2-1

M 2-3

l34

l45

l23

l12

Column Moments



Simple construction

In general, both Eqs. 6.61 and 6.62 must be examined and satisfied:

Eq. 6.61

Eq. 6.62

flexural buckling about MAJOR axis

with flexural buckling about MINOR axis

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NCCI Simplification

• For columns in simple construction, the first term (i.e. the axial load) of both expressions (Eq. 6.61 and 6.62) dominates.

• For UC sections, Iy > Iz (usually around 3 times greater), so Nb,y,Rd > Nb,z,Rd (greater difference for higher slenderness).

• For practical columnin a storey with no intermediate lateral restraint, Eq. 6.62 will always govern.

Eq. 6.62

with flexural buckling about MINOR axis

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NCCI Simplification

Given that the moment components are small for simple construction, the interaction factors can be conservatively

simplified

without

any

significant

overall

loss of efficiency, resulting inkzy = 1.0 and kzz = 1.5

Cross-section capacity check is not necessary

Buckling Check for Columns in Simple Construction

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Calculate beam reactions.

Calculate factored axial load (include self-weight) within length of column.

Calculate applied moment from the beams, taking eccentricity into account.

Divide moment between column lengths in proportion to their stiffness ( EI / L).

Perform Buckling Check:

Design Procedure

k

values

simplify

tokzy = 1,0; kzz = 1,5

Note on the use of simplified equation:

1 Normally, bucking

length

should

be

based

on

storey height

2 Avoid class 4 section



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Examples



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Example BC-3: UC in simple construction

The figure on the right shows a multi–storeysimple structure. You are required to check the

adequacy of the column betweenlevels 1 and 2

using UC 203x203x46 in S275 steel.

5000

3000

Level 1

Level 2

Level 3

F C 2

Factored Loads(self weight is already included)

F C 2= 410kN

R1 = 40kN

R2 = 160kN

R3 = 30kN

R3

R1

R2



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Axial Loads

Maximum axial load at the level 1 which includes self weight of columnSW = 1.35*5*46.1*9.81 = 3kN

F C 1=F C2+ R1+ R2+ R3+SW = 410+40+160+30+3 = 643kN

R3

R1

R2

y

y

z z

Moments at Level 2

Stiffness of column between level 1 and 2 = EI /5

Stiffness of column between level 2 and 3 = EI /3

Ratio of stiffness = 5/3 = 1.67 > 1.5

Distribute moments in proportion to their stiffness

Distr ibut ion of Moments to the Columns at Level 2

Note: the shorter (larger 1/ L), stiffer (larger EI ) member takes greater moments.

32.3kNm

20.0kNm

12.3kNm



Yield Strength

t w

= 7.2mm, t f

= 11mm < 16mm f y

= 275N/mm2

Section Classification

= (235/ f y)0.5 = 0.924

c f /t f = 8.00 < 9 = 8.32 Flange is Class 1

We conservatively assume the critical case of web in compression.cw/t w = 22.3 < 33 = 30.5 Web is Class 1

Section is Class 1

Flexural Buckling about z-z axis

Use buckling curve c = 0.49

Buckling curve a0 a b c d

Imperfection factor 0.13 0.21 0.34 0.49 0.76

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Cross-section Limits Buckling curve

Rolled I-sectionsh/b ≤ 2

h/b > 2

a

b

Buckling curve a b c d

Imperfection factor LT 0.21 0.34 0.49 0.76

Lateral Torsional Buckling

Use buckling curve a

LT = 0.21

M y,21=12.3kNm

M y,12=0kNm



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Only ONE interaction equation to check for columns in simple design.

The cross-section capacity and buckling checks have been combined into one conservative equation.

Buckling Check for Columns in Simple Construction

N ed

(kN) M y,Ed

(kNm) M z,Ed

(kNm) N b,z,Rd

(kN) M b,Rd

(kNm) M z,Rd

(kNm)

643 12.3 0.4 762 121 63.5

Moment Resistance about z-z axis

The column is SAFE.



UC 203x203x46 in S275 steel

L = 5m

Page C-167

.

Buckling Check for Columns in Simple Construction using design table

N ed

(kN)

M y,Ed

(kNm)

M z,Ed

(kNm)

N b,z,Rd

(kN)

M b,Rd

(kNm)

M z,Rd

(kNm)

643 12.3 0.4 762 136 63.5

Page C-78

Page C-167 Page C

‐78

C1 = 1.88 Mb,Rd = 136

The column is SAFE.

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Design of

bracing

frame

• Simple frame cannot resist horizontal loads

• Bracing system

will

resist

all

the

lateral

loads

W + EHF W + EHF W + EHF W + EHF

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Braced Core to provide lateral stability



UE SQUARE

•18 Storey office building

•Steel weight = 1800 tons

•Castellated beams

•Composite slab



CUPPAGE CENTRE

(STARHUB CENTRE)

• Completed in 1998

• Rebuilt 10-Storeybuilding

• Steel weight = 3000 tons

• Composite beam

• Encased composite

column

• Composite slab

• Simple construction

• Core wall with addition

steel braces for lateral

stability



Cuppage Centre

Simple connection



Floor

Diaphragm

simple construction

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