amos curved beam

8/12/2019 AMOS Curved Beam

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Introduction

The beam theory can also be applied to curved beams allowing the stress to be determined for shapesincluding crane hooks and rings. When the dimensions of the cross section are small compared to theradius of curvature of the longitudonal axis the bending theory can be relatively accurate. When this is notthe case even using the modified Bernoulli-Euler only provides approximate solutions

Symbols

ε = strain

e = eccentricity r c - r n! m!c c = "istance from centroid axis to innersurface. m!c i = "istance from neutral axis to innersurface. m!c o = "istance from neutral axis to outersurface. m!

dφ= #urface rotation resulting from bending

stress

σ = stress $%m&!

E = 'oung(s )odulus = σ %e $%m&!

y = distance of surface from neutral surface m!.r n = *adius of neutral axis m!.r c = *adius of centroid m!.r = *adius of axis under consideration m!.

I = )oment of +nertia m, - more normally cm

,!

= section modulus = +%y maxm - more normally

cm!

Theory

The sketch below shows a curved member sub/ect to a bending moment ). The neutral axis r n and the

centroid r c are not the same.This is the primary difference between a straight beam and a curved beam.

The strain at a radius r =

The strain is clearly 0 when r = at the neutral axis and is maximum when r = the outer radius of the beam r= r o !1sing the relationship of stress%strain = E the normal stress is simply.

The location of the neutral axis is obtained from summing the product of the normal stress and the areaelements over the whole area to 0



$eutral 2xis for a *ectangular #ection..

Curved Beam in Bending

The stress resulting from an applied bending moment is derived from the fact that the resisting moment is

simple the integral over the whole section of the moment arm from the neutral axis y! multiplied by σd2 =

d3!. )oment e4uilibrium is achieved if



The curved beam flexure formula is in reasonable agreement for beams with a ratio of curvature to beamdepth of r c%h of 5 6 rectangular section!. 2s the beam curvature%depth radius increases the differencebetween the maximum stress calculated by curved beam formula and the normal beam formula reduces.+f the ratio is about 7 then a maximum stress error of only about 68 results from using the straight beamformulae.

$ote9The above e4uations are valid for pure bending. +n the more normal cases of e.g crane hooks: the bendingmoment is due to forces acting on one side of the section under consideration. The bending moment: in

this case has to be taken about the centroidal axis : not the neutral axis and the additional tensile orcompressive stresses have to be considered to obtain the resultant stresses on the section. see examplebelow!.

Example Hook Calculation

The hook is lifting a load of &6000$.



The stress values plotting against r are shown below9

The tensile stress at the inner surface is calculated at ;&<.< $%mm& and the compressive stress at the

outer surface is calculated at -,&:&6 $%mm&...This section profile results in a tensile stress three times

greater than the compressive stress. 2 more efficient section with the stresses balanced would result fromhaving a wider inner section and a thinner outer section.



Stress In Bars Of Small Initial Curvature.

Where the radius of curvature is large compared to the dimensions of the cross section,

the analysis of stress is similar to that for pure ending.

!et e the initial " unstrained# radius of curvature of the neutral surface and $ the

radius of curvature under the action of a pure ending moment %

&hen the strain in a n element at a distance y from the neutral a'is is given y()"*#

"+#

"#

since

If y is neglected in comparison -ith

"#

/eglecting lateral stress the normal stress

"0#

sustituting in e1uation "#"2#

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&otal normal stress 3 4

"5#

-hich sho-s that the neutral a'is passes through the centroid of the section.

"6#

"7#

"*4#

Comining e1uations "2#and"*4#

"**#

the strain energy of a short length "measured along the neutral surface# under theaction og ending moment % is()

"*+#

"*#

8rom e1uation " 5#"*#

9pplication &o &he :esign Of 9 ;iston $ing



Suppose it is re1uired to design a split ring so that its outside surface -ill e circular in

oth the stressed and unstressed conditions and the radial pressure e'erted -ill e

uniform. If p is the uniform pressure on the outside then the ending moment at e isgiven y()

"*0#

-here d is the depth of the ring in the a'ial direction integrating

"*2#

"*5#

"*6#

"*7#

"+4#

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Which is the re1uired variation of thic<ness =sing e1uation "*2#. &he ma'imum endingstress at any section

"+*#

"++#

-hich has it>s greatest value -hen"+#

"+#

"+0#

-hich determines the initial radius -hen values for are assumed.

Stresses In Bars Of !arge Initial Curvature.

When the radius of curvature is of the same order as the dimensions of the cross section,

it is no longer possile to neglect y in comparison to $ and it -ill e found that theneutral a'is does not pass through the centroid. 8urther the stress is /O& proportional to

the distance from the neutral a'is



"+2#

"+5#

-here y is the distance from the neutral a'is as efore and is the initial d radius of theneutral surface.

8or pure ending the &otal normal force on the cross section 3 4

"+6#

"+7#

"4#

"*#

"+#

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"#

Where e is the distance et-een the neutral a'is and the principle a'is -hich is throughthe centroid " e is positive -hen the neutral a'is is on the same side of the centroid as the

centre of curvature#

Sustituting in e1uation "4#"#

"0#

$earranging

"2#

In this e1uation y is positive measured out-ards, a positive ending moment eing onethat tends to increase the curvature.

$ectangular Cross)section

from e1uation "+6#

"5#

!et ? 3 y ) e 3 the distance from the centroid. 9lso the mean radius of curvature

"6#

"7#




"4#

"*#

"+#

9s e is small compared to and d, itis difficult to calculate -ith sufficient accuracy

from this e1uation and the e'pansion of the log term into a convenient series is of

advantage.then

"#

@'ample *(

Clic< here to e'pand this hidden section 9 curved ar, initially unstressed, of s1uare cross section, has in. sides and a mean

radius of curvature of .0 in. If a ending moment of 4 tons)in. is applied to the ar

tending to straighten it, find the stresses at the outer and inner faces.

"#

"0#

"2#

"5#

"6#

9t the inside face"7#

"04#

"0*#

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9t the outside face

"0+#

"0#

"0#

&he actual stress distriution is sho-n in the diagram.

&rape?oidal Cross)section.

By %oments





"00#

"02#

By putting"05#

"06#

"07#

"24#

"2*#

from -hich

"2+#

and since"2#

@'ample +(

Clic< here to e'pand this hidden section 9 crane hoo< -hose hori?ontal cross)section is trape?oidal, + in.-ide on the inside and *

in. -ide on the outside y + in. thic<, carries a vertical load of 4ne ton -hose line of

action is is +.0 in. from the inside edge of this section. &he centre of curvature is + in.

from the inside edge. Calculate the ma'imum tensile and compressive forces set up.$eferring to the last figure.

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"2#

"20#

"22#

8rom e1uation "2+#

"25#

"26#

"27#

"54#

"5*#

"5+#




"5#

"5#

9t the inside edge"50#

"52#

"55#

&he comined stress 3 .4+ A 4. 3 .0 tonss1.in. tensile.

9t the outside edge

"56#

"57#

"64#

Circular Cross Section




&he analysis follo-s the same method as -as used in the previous section on &rape?oidal

cross sections."6*#

"6+#

"6#

"6#

&o evaluate the aove e'pand

"60#

"62#

"65#

:eflection Of Curved Beams "direct %ethod#If the length of an initially curved eam is acted upon y a ending moment % itfollo-s from e1uation "*4# that)

"66#

But is the change of angle sutended y at the centre of curvature and

conse1uently is the angle through -hich the tangent at one end of the element rotatesrelative to the tangent at the other end.

i.e.

"67#



&he diagram sho-s a loaded ar -hich is fi'ed in direction at 9 and it is re1uired to find

the deflection at the other end B

:ue to the action of % on at C only, the length CB is rotated through an angle"74#

&he vertical deflection of B 3 BB> cos

"7*#

&he hori?ontal deflection of B 3 BB> sin

"7+#

:ue to the ending of all the elements along 9B

&he vertical deflection at B9nd the hori?ontal deflection 3

"7#

@'ample (

9 steel tue having an outside diameter of + in. and a ore of *.0in. is ent into a1uadrant of 2ft. radius. One end is rigidly attached to a hori?ontal ase plate to -hich the

tangent at that end is perpendicular. If the free end supports a load of *44 l. , determine

the vertical and hori?ontal deflection of the free end.

"7#




"70#

"72#

"75#

"76#

Dertical deflection 3

"77#

"*44#

"*4*#

Eori?ontal deflection 3"*4+#

"*4#




"*4#

:eflection 8rom Strain @nergy " Castigliano>s &heorem#

&heorem If = is the total strain energy of any structure due to the application of e'ternalloads

"*40#

and to the couples ...then the deflections at ...in the directions

... are and the angular rotations of the couples are

at their applied points.

;roof for concentrated loadsIf the displacements " in the directions of the loads# produced y gradually applied loads

"*42#

!et alone e increased y

then"*45#

"*46#

"*47#

-here

"**4#

But if the loads

"***#

Sutracting e1uation " *46 # and neglecting the products of small 1uantities

"**+#

Sutracting e1uation " **4 #"**#

"**#



Similarly for and the proof can e e'tended to incorporate couples.

It is important to stress that = is the total strain energy, e'pressed in terms of loads and

not including statically determinate reactions and the partial derivative -ith respect to

each load in turn " treating the others as constant# gives the deflection at the load points inthe direction of the load.

&he follo-ing principles should e oserved in applying the theorem

*# In finding the deflection of curved eams and similar prolems, only strain energy dueto ending need normally e ta<en into account

"**0#

+# &reat all loads as variales initially carry out the partial differentiation and integration

and only putting in numerical values at the final stage.# If the deflection is to e found at a point -here, or in a direction there is no load, a

load may e put in -here re1uired and given a value of ?ero in the final rec<oning

Fenerally it -ill e found that the strain energy method re1uires less thought inapplication than the direct method, it eing only necessary to otain an e'pression for the

ending moment also there is no difficulty over the 1uestion of sign as the strain energy

is ound to e positive and deflection is positive in the direction of the load. &he onlydisadvantage occurs -hen a case such as mentioned in note aove has to e dealt -ith

in -hich case the direct method -ill proaly e shorter.



High Rise Buildings - Design Issues and Concerns

This paper deals with specific issues related to building analysis and design. This paper aims at creating

awareness among designers, construction managers and architects on issues affecting - performance, structural

efficiency and economy of buildings. Issues of configurations, torsion in buildings, its implications on various

elements, limitation of existing methods and alternate methods for estimation of fundamental frequency,

temperature effects and various parameters affecting analysis and design are discussed. Based on specific

experiences gained by authors, a methodology has been put forward for dealing with various concerns. A broad

comparison among various software pacages has also been presented.

Introduction! "igh rise buildings have become order of the day in a #er of moment in metropolitan cities. $uch

fast pace has not only necessitated the requirement of understanding the developments in the field of high rise

buildings bur also to understand the issues contextually. This paper is an attempt to address specific issues

related to structural behavior, analysis % design and suggest specific guidelines.

Classification of Structural systems !The issues that are of significance in high rise buildings are a&. 'ateral

load resistance, b&. 'oad carrying capacity Based on the ref ()&, following is the summary of structural systems.

*ven though, subsystems presented below in +ig ).) are rarely independent, effort shall be to integrate framing

elements into lateral force resisting elements to achieve efficiency and economy.

lassification shown in +ig ).) has four levels namely, +raming systems, Bracing systems, +loor framing systems

and Building configuration % load transfer systems. +raming systems include bearing walls are used for low rise

buildings while core and frame systems are usually adopted for low and medium rise buildings. Tube is used for

medium to high rise buildings.

'evel I. systems require appropriate bracing systems to resist lateral forces to control drift and to add ductility

to #oints when buildings become high rise. "ence bracing on each plane becomes essential.

Appropriate structural systems! +ig )./ and +ig ).0 shown below summari1es two district ways of

classification of systems for tall buildings

2pto )3 floors $emi rigid frames

+or )3 to 04 floors 5igid frames

04 to 34 floors +rames with shear truss systems

34 to 64 floors +rame with shear band and out rigger trusses

64 to 63 floors *nd channel framed tube with interior shear trusses

63 to 74 floors *nd channel framed tube with middle framed tubes

74 to 84 floors *xterior +ramed Tube

84 to ))4 floors Bundles framed Tube

))4 to )/4 floors *xterior 9iagonalised Tube

Today, we have buildings which are as tall as )444m and the height of building is still going up. +or high rise

buildings, level A to 9 can be understood through experimental model studies. +or medium % high rise buildings

where experimental studies are not carried out and dependent on only analysis, we need to understand the

issues in 'evel and 9.

Configuration Issues! :e always wonder; 9o we understand our buildings ;. :e analyse buildings and design

elements lie slab, columns and beams assuming that all elements of the building acts together continuously.And, when earthquae comes, we generate a theory for failures. If the above analogy is true, ; then why a

branch of a tree shall fall instead of whole tree <;

If the above argument is correct, the same analogy may be applied for buildings. +or example, we have

structure representing the tree. "owever, the trees stiffness is uniformly reducing as per laws of nature and

stability. :e do not find a large branch coming out at higher levels as that of our buildings. In the present

situation, architects want large cantilevers and hanging structure etc. at higher levels.

$o, inherently, we are creating a disharmony into the structure and woring against the laws of nature. "ence

there is a role for engineer to solve the created problem. =ur experience shows, while dependency on

interpretations and software is inevitable, #udicious and common sense approach is warranted. ase studies



discussed below explain the inadequacies in analysis and impact on stability arid cost of the pro#ect.

Typical Layout & Configuration Issues ! I$ )>80-/44/ (riteria +or earth quae 5esistant 9esign of

$tructures & discusses certain plan forms with re-entrant corners. These are torsionally sensitive. "ence code

has a special mention about them. "owever, the built forms used in several metropolitan cities are equally

sensitive to torsion , despite their symmetrical form.

The built form shown above is a typical example used in practice. This plan has many re-entrant corners and

importantly, rigid blocs are connected by wea corridors. In this case, corridors stability will be based on the

width of corridor in proportion to width of the building as by virtue of its position, the same will be sub#ect to

large shear and axial forces.

It may be the case that regular analysis carried our by designer may not be able to capture specific issues in

such buildings. 9espite symmetry, such buildings tend exhibit totally a different behavior under load variations

which may not be uniform for all buildings. "ence, it is advisable to completely detach the blocs if base

dimensions are satisfactory (as shown alternative ) of +ig /./& or connect the building through open corridors to

enable the building to act as a single element.

5eferring to the plan given below (+ig /.0& three blocs are staggered in plan and connected by corridors. Issues

in such plans are

• Blocs are virtually dis#ointed except fragile connections at corridors.

• 9istinct mass and stiffness centers of each bloc c&. rincipal movement direction during under earth

quae could be different for each bloc.

As can be seen from the conventional analysis, such forms are torsionally prone, hence their synchroni1ed

behavior cannot be expected under seismic forces. $uch uncoupled movement has the potential to dis#oint the

structure at wea planes (in this case corridors&. "ence, separating the blocs is appropriate. "owever, if the

blocs have to be connected, more involved methods of analysis are required. oncerns related to seismic

pounding etc. need to be taen care in the detailing.

Torsion based Issues! 9ue to difference in mass and stiffness centers, torsion is generated! :hen torsion is

generated in buildings, failure mechanisms will be different. A review of the case presented here below explains

the issue. 5ef fig. /.? below. After carrying multiple analysis using member modeling, following observations are

made.

• $eismic oefficient method is not suitable as layout is torsionally prone

• 5esponse spectrum method indicated torsion

• 9ue to torsion, member modeling analysis is inadequate.

The above points are evident from mode shape shown in +ig. /.?. "ence stiffness ad#ustments in terms of

column locations and orientation are carried out. +ig /.3 shows mode shape after ad#ustments. 9ifference

between the two models shown in fig /.? % /.3 is the change in mode shape pattern. In the second one,

translational mode is more uniform which is desirable. This modified mode shape also indicated better mass

participation factors. As shown below, such modifications have influence on slabs also. "ence, +*@ analysis was

c arried out.

Moments in Slab! 5emars By ad#usting the stiffness, we could reduce the stresses in slabs considerably.This

has not only led to improved structural behavior but also to economy.

$tiffness Ad#ustment 2sing $hear :all In the case presented here below, due to torsion, composite shear wall is

considered. 'ocation of the shear wall was derived using trial and error method. As can be seen from fig 0./ %

fig 0.0, there is a considerable reduction in column steel due to reduction in imaginary moments generated out

of torsion.

omposite shear wall is made of 5 and bric. Interface stresses are looed into.

Remarks : =f the several ways and means available for torsion ad#ustment, integration of available

components, lie walls , lift shafts into building improves the structural performance



and efficiency.

P!elta Analysis! :hile I$ )>80-/44/ specifies use of delta analysis for seismic loads. It is a suggested

methodology even for gravity loads as model errors, effect of lateral displacements due to torsional effects will

become evident by adopting delta analysis. Issues connected to delta analysis are

• delta is different from perform analysis

• $pecial load combinations to be used for p-d analysis

• 9ynamic analysis automatically considers p delta effects

• +or normal height structures, it is not critical

• 'oad factor for delta effects need to be for serviceable loads. "ence using the same for non uniform

load factors is not possible. :hen the load factors are not uniform (for ex! under 9'* load, load

factors are ) and 4.8 respectively&. 2nder such conditions, forces obtained from delta analysis cannot

be magnified directly.

• If iterations do not converge, building is liely to be unstable.

Member "ffsets! As per I$ ?36, moments in beams shall be considered at the face of columns even for

carrying out analysis. By using member offset, this effect can be considered. 2sing this command, additional

moment generated by shear which is acting at the face of the column is added to original moments and analysis

is done. In some cases, the assumption that the ends of a beam element are located at the end nodes is

inaccurate. A typical example is a shear wall with openings forming hori1ontal beamsC the span of the beams

should be measured from the face of the walls rather than from the wall center where the end nodes are located.

The effect on the beam results can be significant when this ;offset; length (one-half of the wall width in this

example& is large compared to the beam length art of the beam framing into column is assumed to be rigid and

can transfer the moment without any displacements.

*ven though software have provision for beam offset as well as column offset, the disadvantage in column offset

is that large imaginary moments get generated at footing level which- is not correct as node at base is shifted.

Beam offset does not solve the placement of column at its center of gravity. Another method is to place column

at its physical center and create a rigid lin between beam face and column center. 5ef fig below.This method is

advisable as accuracy of the center is ensured fully. Analysis time increases tremendously.

#ffect of infill $alls! Infill walls influence both lateral movement and +undamental time period. :hen lateraldrift exceeds the limit, adopt +*@ or grillage analogy to analyse the structure. If the structure still has a large

drift, adoption of shear walls or suitable methods may reducing the drift.

Time period estimation! lause 7.6.) of I$ )>80-/44/ specifies method for fundamental time period for 5

frames and 7.6./ for structural frames with infill walls. :hile 7.6./ is generali1ed for all configurations, it may

not be true for all cases.

An alternative method is suggested to estimate time period using realistic representation of infill walls. 2sing

grillage analogy for the purpose, for a typical stilt 3 structure shown in +ig 7.), estimated time period is as

follows!As can be seen from the table 7.), time period using the grillage analogy in principle is different in both

directions indicating that structures are more flexible than what the code estimates. The difference is around

/3D in one direction and )0D in the other. It is evident that the codal provisions stipulated will not be able

capture the time period accurately for buildings which are other than rectangular bloc. "ence, proper

estimation of time period is essential as seismic forces are a +unction of time period.

Rigid Links! 9iaphram action is considered by ridgid lins. rogram expects rigid diaphram action which is

seldom possible due to inadequate thicness of slab. If torsional modes are predominant, do not consider rigid

lin concept but use +*@.

#ffect of Retaining %alls for Multiple basements! Eormally, when retaining walls are provided in basement

and connected to slabs, it is important to consider the effect of the same. $tiffness of floors considerably

increase in the presence of retaining walls. Also the missing mass will playa considerable role as the building

goes through retaining walls in basement, no walls in stilt and again infill walls in upper floors. roper location



and detailing of control #oints and expansion #oints are essential while designing retaining walls.

Metods for Impro'ing !uctility

• Adopt wide beams than columns

• ombination of capital in beam slab construction

• onfinement concepts. such as capping for column-beam #unctions

• Additional ties in columns and stirrups in beams as per I$ )08/4

• lacing the beam steel in extended width of beam is permissible upto 0 times depth of slab thicness

for intermediate beams and upto width of column for external beams (5ef >&

#ffects of Cantile'er Slabs! antilever slabs tend to disassociate from main structure due to vertical

accelerations and independent frequency properties "ence there is a need to integrate cantilevers into main

structure by secondary framing etc. or reducing loads on the same. In a case presented here below, cantilevers

are Fm for an art gallery. "ence, composite virandeel girders are used in place of conventional system to

improve structural integrity.In such cases, it is important to note that construction sequence shall be defined to

achieve composite action.

Column Si(es & Sapes! *arthquae in Fu#arat has taught us many lessons and highlighted inadequacies in

column width and beam-column #unctions etc. 9espite such experiences, designer tend to use slim columns (/44

mm& for high rise buildings. =ne of the inferences of +ig ).0 is inability of pure rigid frames for high rise

buildings. "ence restricting column widths leads to inadequate interaction between columns and framing which

not only affects load carrying capacity but also lateral force resisting mechanism. In other wors, frames tend to

be become unbraced and structural cost becomes prohibitive while adequacy is still an issue. "ence, it is

advisable to adopt provisions for I$ )08/4. These guidelines are similar to international codes of practice.

Alternate Column Sapes: 9ue to provisions in code and availability of large amount of literature, rectangular

columns have become order of the day. "owever, rectangular columns are not structurally efficient due to large

variation in stiffness about ma#or and minor axes. $quare and circular columns are more efficient than

rectangular columns.

+or residential pro#ects, where square and circular columns can not be used, ' columns and T columns are

efficient. It can be seen from many high rise buildings at national and international level, ' columns are

predominantly used.

$ome reports indicate that ' columns in paring floors (without walls& have failed under earthquae because of

torsional sensitivity. "ence, it is advisable to have square columns upto stilt floor to avoid premature failure of

columns. :hen ' columns are used, it is necessary to eep the columns at its centroid and have rigid lins with

main beams.

)raming Systems!:e have conventional beam framing and flat slabs in vogue. 'imitation of both systems

under seismic conditions are well understood. +lat strip slabs systems for large spans (developed by authors& is

a structurally viable alternative over the above and developed based on principles of stress leveling. Typical flat

strip slab system is shown below. It will also eliminate the common problems encountered in conventional

systems and also offer larger column free spans over conventional flat slabs. Based on 5ef () 4&, such wide

strips performed well under lateral loading and the slab participation is better.

Issues in Composite Structural Slabs! In the case presented below, composite steel dec is tuced in

between two concrete towers. =n examination, following points are observed.

• $eismic isolation is not provided. As a result, there is a possibility that dec may get crushed under

earthquae due to pounding from blocs

• 9eflections are more and cause vibrations.

:hen steel structures are made to operate under large deflection, sustained loading will also cause further

deflection (i.e long term deflection& and due to creep. I$ >44 specifies deflection limits with a primary focus on

industrial buildings. There is no specific mention about useable composite floors. "ence deflections shall be as

per 5. As per 5ef ()/&, span to depth ratio is /? or less.



+ollowing guide lines on natural frequency are useful while analy1ing such decs. Based on 5ef ()/&, :hen

natural frequency of the floor exceeds 8-)4 "1, resonance becomes less important for human induced vibration

but floor response foot step need to be analysed ontinuous motion can be more annoying than motion caused

by infrequent impact.

5esponses are more by people when vibration frequencies are between ?-> "1. Above these frequencies, people

accept higher vibration accelerations.

+loor systems with less than 0 "1 should generally be avoided.

Temperature #ffects! As the modern buildings call for expansion #oint free buildings, there is a need to

dispense with expansion #oint. 'iterature indicate buildings constructed upto 84m for unheated buildings and

heated buildings upto )>4m for a temperature difference of /) deg are reported to be functioning

satisfactorily, need for temperature analysis is warranted (5ef )0&.

=ne must be dear that satisfactory performance does not mean crac free structure, location of cracs are

predefined at conspicuous locations and width of crac is significantly reduced by presence of temperature steel.

9ue regards shall be made to shrinage and creep stresses when length is more. Temperature difference of )3

deg for non air conditioned buildings and /3 9eg for air conditioned buildings are suggested.

Building shown below is 73m long and shrinage strip method is adopted to allow shrinage cracs at certain

locations. hysical discontinuity of wall is part of the planning on terrace, membrane water proofing is

suggested as cracing is unavoidable. ases of 044m building without expansion #oint are being considered by

others. In arid 1ones lie ours where temperature variations are predominant, such buildings shall be #udiciously

adopted. It will be a challenging tas to contain cracs in walls. "ence physical discontinuity need to be planned.

Soft Storey #ffects ! As per I$ )>80-/44/, lause 7.)4, columns in paring floors need to be designed for /.3

times storey shears and moments in both beams and columns. It is to be noted that enhancement of moments

and shears shall be done after analysis and not to be included as part of load combination. $oft storey effect is

due to absence of walls in respective floors and random nature of earthquae motion., in other words storey

stiffness variation. It is also observed that through alternate analysis, enhancement is found to be much lower

than suggested by code.

*on Structural #lements! Eon structural elements such as walls, lintels and sunshades etc. require a special

consideration. hand boo for odes on earthquae *ngineering for non load bearing walls. Buildings with walls

on cantilevers, secondary framing to hold the walls is essential. Eo opening shall be permitted close to corners

as wall tend to fall and easy prey for even light tremors. "ori1ontal reinforced mortar bands are required for all

walls on cantilever ends and proper anchoring to main walls is essential.

:here sunshades are provided. on ))3mm walls which are resting on cantilevers, they shall be duly tied to main

beams either by secondary framing or suitable hangers.

9etailing for seismic #oints shall be as per I$ ?0/6 )880 - *arthquae 5esistant 9esign and onstruction - ode

of ractice. Basic principle of seismic #oint shall be to abridge the #oint which is in the order of 73-)34mm or

more without causing physical discomfort for daily use and shall crumble under seismic movement.

%ater retaining structures !:ater retaining structures on terraces shall be suitably be detached or detailed as

they tend to produce opposite force to that of main building due to frequency mismatch. $uitable dampers or

hinges in columns at the main slab level are required.

)ootings at !ifferent Le'els !:henever footing rest at different levels or varying substrata, it is highly

advisable to adopt integrated analysis including footings. +ootings at varying levels has potential for shift of

mass and effect the whole structure

Construction Loads ! $everal slab collapses are reported in the recent past on account of excessive loading



during casting of upper slabs. It is essential to have an idea of construction loads and either design shall have

adequate provision or bac propping shall be specified. In a typical flat slab construction, construction loads

wor out to be ))-)/ E G sqm while slab below is only designed for 3-6EGsqm."ence there is a immense need

to provide suitable bac propping. In the absence of proper calculations, at least two lower slabs shall be

supported. :hile slab below shall have full supports, /nd slab shall have at least 34D of required props.

Comparison of Soft$are+ Brief comparison among various software available in made. These comparisons are

based on out experience and based on discussions with respective developers.

Conclusions

• +rom the above discussion, it is clear that analysis results can not be adopted directly for design as

issues lie torsion etc. affect the building.

• @odeling shall be such that so to achieve the desired behavior into be structure.

• 9esign methodology is to be chosen as per pro#ect requirement.

• Based on pro#ect demand, appropriate software shall be chosen.

• $oftware provisions need to be understood clearly.

• +or high rise buildings, more than one software shall be adopted to predict structural behavior for

ensuring fool proof results.

References :

• $tructural systems for Tall buildings - ouncil on Tall Buildings % urban "abitat - @c Fraw"ill

International *dition, )883

• I$ )>80 (art )& -/44/ - riteria +or earth quae 5esistant 9esign of $tructures (an ) ! Feneral

provisions and buildings&

• *dward ' :ilson - $tatic % 9ynamic Analysis of $tructures - A hysical Approach with emphasis on

*arthquae *ngineering-, IH edition, omputers % $tructures, Inc., /44?

• +arheed Eaeim - The $eismic 9esign "and Boo - Han Eostrand 5einhold, Eew or, )8>8

• I$-?36-/444 lain % 5einforced oncreteode of ractice

• $ $urana, 5 Agarwal ., Frillage Analogy in Bridge 9ec analysis Earosa ublishing "ouse, )88>

• I$ )08/4-)880- 9uctile detailing of 5einforced oncrete $tructures $ub#ected to $eismic +orces- ode

of ractice

• 9esign % onstruction of $eismic 5esistant 5einforced oncrete +rame and $hear wall buildings -

2EI9=G 2E9p, )88?

• 9esign of 5 columns - 9r. $inha , @c Fraw "ill ublications

• HH 5angarao % E H 5amana 5ao - +lat $trip $lab system for 'arge $pan Buildings -aper presented at

:orld =fInnovation in $tructural *ngineering held at "yderabad, India, /44?

• James @ 'a+ % James K :ight-)888;5einforced oncrete *xterior :ide Beamolumn- $lab onnection

$ub#ected to 'ateral 'oading; - AI $tructural Journal B.86, E=.?, July-August, /44)

• +loor Hibrations 9ue to "uman Activity ($teel design Fuide $eries& - American Institute of $teel

onstruction Inc. % anadian Institute $teel onstruction

• @ar +limel - "and boo of oncrete *ngineering (/nd edition& B$ ublishers % 9istributors, )8>6

• $-// - *xplanatory hand boo for odes on earthquae *ngineering

• I$ ?0/6 -)880 - earthquae resistant 9esign and onstruction - ode of ractice

• orrespondence % @anuals from $oftware developers

Q. How can you drop a raw egg onto a concrete floor without cracking it?

A. Concrete floors are very hard to crack! (UPC opper"

Q. #f it took eight $en ten hours to %uild a wall& how long would it

take four $en to %uild it?



A. 'o ti$e at all it is already %uilt. (UPC ) *ank +pted for #,"

Q. #f you had three apples and four oranges in one hand and four

apples and three oranges in the other hand& what would you have?

A. -ery large hands. (ood one" (UPC // *ank +pted for #P"

Q. How can you lift an elephant with one hand?

A. #t is not a pro%le$& since you will never find an elephant with one

hand.

(UPC *ank /0 +pted for #1"

Q. How can a $an go eight days without sleep?

A. 'o Pro%s & He sleeps at night. (UPC #A *ank 23"

Q. #f you throw a red stone into the %lue sea what it will %eco$e?

A. #t will 4et or ink as si$ple as that. (UPC #A *ank "

Q. 4hat looks like half apple ?

A5 he other half. (UPC 6 #A opper "

Q. 4hat can you never eat for %reakfast ?

A5 7inner.

Q. 4hat happened when wheel was invented ?

A5 #t caused a revolution.

Q. 8ay of 8engal is in which state?

A5 9i:uid (UPC ))*ank "

amos curved beam

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