i Optimisation of Lateral Load

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LATERAL LOAD RESISTING SYSTEMS FOR HIGHRISE

BUILDINGS USING ETABS


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A

Report on

Thesis submitted in partial fulfillment of the requirement for the award of the degree of

Master of Technology

In

Branch Na!e""

Submitted By

>

>

Under the Esteemed Guidance of


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#ERTIFI#ATE

#ollege Logo ""

This is to certify that the Thesis entitled 3title of the project""0 is being submitted by

>bearing Roll number""in partial fulfilment of the requirement for

the award of the degree of 45Tech in


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Ne4t 2age5 This page is required for the candidates who pursue the project wor!

outside 'other

organi7ation)& under the super+ision of an E3TERNAL GUIDE. This page is another

certificate

gi+en on the organi7ation letterhead where the project wor! is pursued& which should be

certified

and duly signed by the 89ternal guide about wor! done by the candidate and clearly

mentioning the duration of the project wor!5 The format for this page will almost be the

same as the pre+ious page with double spacing between the lines5

$or+

.nclude the #eclaration page in the below specified :ormat;


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DE#LARATION

. St)&ent Na!e""bearing Roll N)!6er Roll No""& a bonafide student of


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Ac8no(le&ge!ent

. would li!e to e9press my sincere gratitude to my ad+isor& G)%&e Na!e""&whose !nowledge and guidance has moti+ated me to achie+e goals . ne+er thought

possible5 e has consistently been a source of moti+ation& encouragement& and

inspiration5 The time . ha+e spent wor!ing under his super+ision has truly been a

pleasure5

. than! 55# HOD Na!e""for his effort and guidance and all senior faculty

members of $S8 #epartment for their help during my course5 Than!s to programmers

and non,teaching staff of $5S58 #epartment of =.TS5

. Than! my principal-RIN#I-AL NAME""and 4anagement for pro+iding

e9cellent facilities to carry out my project wor!5

:inally Special than!s to my parents for their support and encouragement

throughout my life and this course5 Than!s to all my friends and well wishers for their

constant support5

Na!es of St)&ent $roll n)!6er+

9ey(or&s


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Belt,truss& Bracings& $omposite building& $omposite structure& #eflection& 8arthqua!e

loads& :inite element modeling& igh,rise& ori7ontal force& %ateral displacement& %ateral

loads& lateral bracings& 4ulti,storeys& utriggers& R$$ shear walls& Seismic action&

Storey drift& Transformed properties& ?ind actions

ABSTRA#T


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The use of composite structures in buildings is time effecti+e& cost efficient and

pro+ides column,free space5 $omposite construction technology is gaining popularity

among builders& contractors and de+elopers not only in .ndia& but throughout the world5

Academic research on this subject mainly focuses on either reinforced concrete or

structural steel buildings5 8+en though studies of indi+idual composite elements of

structure 'such as composite columns and composite beams) are in abundance& there is a

scarcity of research related to the structural performance of composite buildings as a

complete structure5 The ci+il6structural engineer has to go through a lengthy process of

modeling and detailed calculation to find out the requirements of belt,truss and outriggers

and to establish locations of these in buildings5 ence& this topic needs to be in+estigated

thoroughly at the academic le+el to be able to occupy an absolute position in standards

and codes of practice5 This research was carried out by using :inite element modeling of

building prototypes with three different layouts 'rectangular& octagonal and %,shaped) for

three different heights '@ m& 1C m and 1@@52 m)5 =ariations of lateral bracings '+aried

number of belt,truss and outrigger floors and +aried placements of belt,truss and

outrigger floors along model height) with R$$ 'reinforced cement concrete) core wall

were used in composite high,rise building models5 4odels of composite buildings were

then analy7ed for dynamic wind and seismic loads5 The effects on ser+iceability

'deflection& storey drift and frequency) of models were studied5 The best model options

among analy7ed models were outlined with respect to belt,truss and outrigger placements

and hori7ontal loadings5 Analytical models were proposed using a ma9imum height

model for prediction of deflection5 .t was found out that pro+ision of top le+el single floor

belt,truss and outrigger would be +ery beneficial for buildings up to 120 m height& if

subject to seismic load whileD under wind loads& pro+ision of belt,truss and outriggers at

mid,height would pro+ide better displacement control5 4ulti,storeys between 120 m to

/00 m height respond well with single floor bracings placed at /6Erd building height

'measured from base)5 owe+erD if a le+el of double floor lateral bracings was needed

then bracings wor!ed well at the top le+el of the building with critical earthqua!e

loadings5 .t was also obser+ed that staggered le+els of outriggers& i5e5 two or three single

truss floors at +arious heights such as mid,height and /6Erd height 'measured from base)


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of building rendered better lateral deflection control than double floor belt,truss and

outriggers in buildings between 120 m to /00 m height5

Ta6le of #ontents


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Feywords

Abstract5

Table of $ontents

%ist of :igures

%ist of Tables

%ist of Abbre+iations

#HA-TER :5 INTRODU#TION

151 -rologue

15/ -erspecti+e of thesis topic

15E "aps in academic wor!

15 Aim and objecti+es

152 Thesis outline

#HA-TER ;5 LITERATURE RE


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/551 .nception of composite construction

/55/ $ase studies

/52 -rofiled dec!ing as a permanent form

/5G +er+iew of framing system used in this study

/5C $onclusion

#HA-TER >5 STRU#TURAL MODELLING

E51.ntroduction

E5/ Analytical -rogramme and sol+ers for thesis 4odels

E5/51 -rogramme6software selection

E5/5/ Sol+ers used in thesis

E5/5/51%inear static sol+er

E5/5/5/Natural frequency sol+er

E5/5/5ESpectral response

E5E %oads on 4odels

E5E51 "ra+ity loads

E5E5/ %ateral loads

E5 Selection of parameters to satisfy thesis objecti+es

E551 Aims

E55/ -arameters

E55/514odels heights selection

E55/5/%ayout selection for models


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E55/5Eutriggers pro+ision in models

E52 Structural Setup of 4odels

E5251 -rototype set,up in StrandC

E525151$onstruction type

E52515/=ertical support

E525/ Transformed properties for composite elements

E525/51$omposite column

E525/5/$omposite slab

E525E $ore wall6shear wall arrangements

E525 Structural steel elements

E5G Analysis of Results

E5C ptimi7ation procedure

E5 4odeling =alidation

E5@ $onclusion

#HA-TER ?5 =IND A#TIONS ON BUILDINGS

51 .ntroduction

5/ ?ind

5E Aim and scope of 4odeling for wind load analysis

5E51 Aims

5E5/ Scope

5E5E $ompliance with standards


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5 determination of wind action type

52 $hoice and $alculations of ?ind =ariables for models

5251 Selection of wind region

5G $alculation of wind pressure

5C application of wind loads on models

5 ?ind load input in models

5@ :84 Analysis and utput

5@51 4odel analysis

5@5/ 4odel output

510 $omparison and discussion of output

51051 Stiffness ratios

5105/ "raphical representation of output

5105E $omparison of output

5105E51 -ercentage deflection reductions

5105E5/ The frequency increments;

511 $onclusion

#HA-TER @5 SEISMI# A#TIONS

251 .ntroduction

25/ 8arthqua!e6Seismic Actions

25E %imitation and scope of 4odeling

25 -rocedure for calculation of earthqua!e forces


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252 parameters for models

25251 Selection of importance le+el for models

2525/ Selection of site ha7ard factor for models

2525E Selection of probability of occurrence for models

2525 Selection of sub,soil class for models

25252 Selection of earthqua!e design category for models

25G #ynamic Analysis methods for 4odels

25G51 #escription of dynamic analysis

25G5/ Selection of seismic analysis methods for modeling

25C Application of seismic actions on 4#8%

25C51 ori7ontal design response spectrum 'S)

25C51514anual force input

25C515/Auto,generated seismic load

25C515E $omparison and agreement of manual and auto,generated loads5

25C5/ Site,specific response spectra

25 4odel utput

2551 ori7ontal design response spectrum 'S)

255/ Site,specific design response spectra 'SS)

25@ output results in graphical form

25@51 ori7ontal #esign response spectrum 'S)

25@5/ Site,specific design response spectra 'SS)


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2510 $onclusion

#HA-TER 5 RESULTS AND #ON#LUSION

G51.ntroduction

G5/ Summary of results

G5E Best option Selection

G5E51 Basis of option selection

G5E5/ Best model option

G5 Selection of prototype for Analytical model

G52 Analytical model based on ma9imum height prototype

G5251 89amination of ma9imum height models for analytical comparison

G525/ Rationali7ation

G525E -roposal for analytical model

G5G :uture research prospects

REFEREN#ES

L%st of F%g)res


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:igure /51 $apital "ate , Abu #habi

:igure /5/ Tianjin "oldin :inance 11C Tower

:igure /5E-rofile sheeting as permanent formwor! in composite slab

:igure /5Typical outrigger and belt,truss

:igure /52Basic +iew of out riggers and belt truss& ele+ation and plan

:igure E518tabs opening page

:igure E5/ Runner sculpture& Sydney& Australia

:igure E5EBeijing National Aquatic $entre& $hina

:igure E5Terminal /8 of $harles de "aulle Airport& -aris& :rance

:igure E52 %inear static sol+er

:igure E5G Natural frequency sol+er

:igure E5CSpectral response sol+er

:igure E55%oads on model

:igure E5@Basic figure of gra+ity load flow

:igure E510Rectangular model ele+ation 'full model and shear wall)

:igure E511ctagonal model ele+ation 'full model and shear wall)

:igure E51/ %,Shaped model ele+ation 'full model and shear wall)

:igure E51Eutriggers and belt truss

:igure E51 Slab and column composite sections

:igure E512 Beam& column and shear wall arrangement and beam end releases

:igure E51G Support6restraints at base


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:igure E51C Abstract from composite column spread sheet

:igure E51 $omposite slab 'abstract from Appendi9 $)

:igure E51@ $ore layouts

:igure 51 :orce on rectangular layout

:igure 5/ :orce on %,shaped layout

:igure 5E :orce on octagonal layout

:igure 5 #iagrammatical representation of wind calculation method

:igure 52 ?ind Regions of .ndia

:igure 5G Along,wind and crosswind on structure

:igure 5C Abstract from wor!sheet; along,wind force calculation5

:igure 5 %inear wind pressure on :84 4odel

:igure 5@ Application of wind on model in 8tabs

:igure 510 Along,wind linear force on Rectangular 4odel 'partial model)

:igure 511 Along,wind linear force on octagonal model 'partial model)

:igure 51/ Along,wind linear force on %,shaped model 'partial model)

:igure 51E #eflection comparison of / storey models

:igure 51 :undamental frequency of / storey models

:igure 512#eflection comparison of / storey models5

:igure 51G :undamental :requency of / storey models

:igure 51C #eflection comparison of 2C storey models

:igure 51 :requency comparison of 2C storey models


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:igure 251 Seismic action design procedure

:igure 25/ 8arthqua!e a7ard map 'partial) from .S

:igure 25E 8arthqua!e design category5

:igure 25 Abstract of e9cel sheet from distributed base shear table for each le+el '/

storey %,shaped)

:igure 252 Nodal force in H,direction on a typical storey in %,shaped model

:igure 25G "raphical representation of non,structural mass on typical %,shaped model

:igure 25CAuto,Seismic load case generation

:igure 25 Soil,sub class in .S5

:igure 25@ Spectral response cur+e for soil,subclass $e

:igure 2510 Site,specific design response spectra in 8tabs

:igure 2511 #eflection comparison of / storey model 'S)

:igure 251/ #eflection comparison of / storey model 'S)

:igure 251E #eflection comparison of 2C storey model 'S)

:igure 251 #eflection comparison of / storey models 'SS)

:igure 2512 #eflection comparison of / storey models 'SS)

:igure 251G #eflection comparison of 2C,storey models 'SS)

L%st of Ta6les


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Table E51 4odel arrangements

Table E5/ 4odels structural arrangement

Table E5E $olumn si7es of / storeys '@50 m)

Table E5 $olumn si7es of / storeys '1C50 m)

Table E52 $olumn si7es of 2C,storeys '1@@520 m)

Table E5G Structural steel section in models

Table E5C ?ind load cases

Table E5 Seismic load cases

Table E5@ Summary of modeling +alidation for /, storey octagonal model '@50 m)

Table E510 Summary of modeling +alidation for /, Storey %, Shaped model '1C50 m)

Table E511 Summary of modeling +alidation for 2C, Storey rectangular model '1@@520 m)

Table 51 Results for rectangular models

Table 5/ Results for octagonal model

Table 5E Results for %,shaped model

Table 5 4odels stiffness ratios of plan dimensions to height

Table 52 -ercentage reduction in deflection

Table 5G -ercentage increment in frequency

Table 251 Seismic load combination

Table 25/ Results for rectangular models 'S)

Table 25E Results for octagonal models 'S)

Table 25 Results for %,shaped models 'S)


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Table 252 Results for rectangular models 'SS)

Table 25G Results for octagonal models 'SS)

Table 25C Results for %,shaped models 'SS)

Table G51 -lan dimension to height ratios

L%st of A66re*%at%ons


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A I plan area 'm/)5

AcI area of concrete5

AgI gross area of section5

AST I area of steel5

Awall I cross,sectional area of shear wall 'm/)5

b I breath of plan layout 'm)5

$'T) I elastic site ha7ard spectrum5

$d'T) I hori7ontal design response spectrum as a function of 'T)5

$fig&e I e9ternal component was selected for structures ha+ing 3h > /2mJ5

$p&i I internal component selected for 3All walls are equally permeableJ5

$K$ I $omplete Kuadratic $ombination5

d I depth of plan layout 'm)5

8 I elastic modulus '4-a)5

8 I site ele+ation abo+e mean sea le+el5

8cI elastic modulus of concrete5

8sI elastic 4odulus of steel5

8T I elastic modulus of transformed section5

f I frequency '7)5

:8A I :inite 8lement analysis5

:84 I :inite 8lement modeling5

fnI natural6fundamental frequency5


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" I gra+itational loads5

"iI permanent action i5e5 self weight or dead load5

I building height 'm)5

floorI floor to floor height 'm)5

hiI of ithle+el abo+e the base of structure in meters5

S I hori7ontal design response spectrum5

! I stiffness 'kN

m )5

! I e9ponent dependent on the fundamental natural period of structure5

FaI area reduction factor5

Fc&eI combination factor applied to e9ternal pressure

Fc&iI combination factor applied to internal pressure5

!:&iI seismic distribution factor for the ithle+el

FlI local pressure factor5

FpI porous cladding reduction factor5

!pI probability factor appropriate for the limit state under consideration5

m I mass '!g)

4hI hill shape multiplier

4leeI lee effect multiplier considered

47&catI height and terrain multiplier

n I no5 of le+els in structure


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KiI imposed action 'li+e load)5

R$$ I reinforced cement concrete

SpI structural performance factor

SpI structural performance factor5

SRSS I Square Root of Sum of Square5

SS I site specific design response spectrum

(B I (ni+ersal Beam

($ I (ni+ersal column

= I base shear '!N)

?B I ?elded beam

?$ I ?elded column

?iI seismic weight at ithle+el '!N)

?jI seismic weight of structure or component at le+el j '!N)5

?tI total seismic weight of building '!N)5

?9I wind in L,direction5

?yI wind in H,direction5

L,dir5 I L,direction5

H,dir5 I H,direction5

M I earthqua!e ha7ard factor5

M I earthqua!e ha7ard factor5

I StrandC seismic factor related to base shear5


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I structural ductility factor5

O I E5112@/G2E25

I structural ductility factor 'I mu)5

c

I imposed action 'li+e load) combination factor5

PIdeflection 'mm)5

=inter,storey drifts 'mm)5

c I density of concrete5

s I density of steel5

T I density of transformed section5


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#HA-TER :

INTRODU#TION

:.:-ROLOGUE

This thesis aims to study the effect and outcomes of hori7ontal force applied to

composite multi,storey braced frame structures5 The bracing is pro+ided in the form of a

concrete wall& structural steel belt,truss and outriggers5 The study has been carried out by

using the latest computer modeling technology& :inite 8lement 4odeling ':84)5

:.;-ERS-E#TI


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circular& rectangular and square columns and the in+estigations by scientist and researcher

continue5 Het there is a huge lag of scholarly items on the o+erall beha+ior of buildings

constructed using composite slab& beam and columns5 4oreo+er& academic literature

concentrates on the characteristics and properties of wind and earthqua!e loadings5 The

structural designer has to go through a lengthy process of modeling a whole building

prototype as there are no set procedures for finding out the requirements of outriggers and

establishing the location of these in buildings5 The procedure is usually based on trial and

error as well as past e9perience5 .f a project is delayed or cancelled& the e9tensi+e wor!

already performed to establish the feasibility of the project and the initial cost estimation

can go to waste5 Therefore& this thesis aims to study the beha+ior of composite buildings

braced with shear walls and steel trusses under hori7ontal loads5 This will not only be

ad+antageous in the formulation of basic principals or rules for typical building structures

within the scope of .ndian standards& but will also help ci+il6structural engineers in their

routine calculations of cost and material estimation at the conceptual6preliminary stage of

the project5

:.?AIM AND OB'E#TI


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The model +erifications are carried out and finally results are e9tracted and compared and

conclusions are drawn5

:.@THESIS OUTLINE

The thesis consists of si9 chapters& inclusi+e of chapter 15 .t pro+ides a detailed

re+iew& description& calculation and analysis of the selected topic through the chapters

outlined below5

$hapter 1 sets aims and objecti+es of thesis5 .t gi+es introduction of wor! performed

in succeeding chapters to achie+e targets of this study5

$hapter / pro+ides a detailed re+iew of construction in the conte9t of composite

buildings and their historical and modern bac!ground5 A re+iew of a+ailable literature for

composite construction is conducted5 The bracing system popular in composite

construction is described5 The pro+ision of concrete core wall coupled with outriggers

and belt,truss is scrutini7ed in detail with respect to the thesis modeling5 The chapter also

gi+es an account of research on the lateral6hori7ontal loads applied to buildings5 The

loads that mainly affect multi,storey constructions are wind and seismic loads5

$hapter E describes the setup of models5 .t includes calculations of transformed

properties of composite elements5 The range of layouts and prototypes& adopted +ariations

of belt,truss and outriggers& disparity of storey heights and different layouts are

described5 The 8tabs and method of computer analysis are e9plained5 "ra+ity loads for

multi,storey buildings are also discussed in this chapter5

$hapter co+ers wind load and choice and justification of load type 'i5e5 static or

dynamic)5 The +ariables and their rationali7ation are selected for analysis& and the

.ntroduction calculations specific to prototypes and load application in the programme

'8tabs) are summari7ed5 The results are then e9tracted and gi+en in tabulated format& and

also represented graphicallyD conclusions from the analysis are presented5

$hapter 2 centres on the topic of seismic load calculation and its application in the

software5 An e9cerpt of +arious parameters and +ariables for earthqua!e actions is

pro+ided& as well as reasons for the selection of these parameters5 $omprehensi+e


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calculations of seismic load within the scope and limitation of .ndian Standard is gi+en5

The results are listed in tables and graphs5 $onclusions are presented at the end of the

chapter5

$hapter G pro+ides the results and conclusions drawn from the research5 The

outcomes of the thesis are pro+ided in the form of the best options for models of

composite buildings under lateral loadings5 4oreo+er& formulae for predicting deflection

are proposed as a product of the rigorous analysis conducted in the thesis5 Suggestions for

future research are recommended and discussed5

#HA-TER ;


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LITERATURE RE


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construction& as well as for the buildings life,span and during its demolition& under all

possible loads and effects and within acceptable ris! limits as set by the society5

According to Fhan '1@C/) the performance of any structure depends upon

following;

%ateral sway criteriaD

Thermal mo+ementsD

Structural and architectural interaction5

The main and primary concern is the stability and reliability of the entire structure

and structural components& as well as their ability to carry applied loads and forces5 Tall

and lean buildings are more susceptible to lateral sway and deflections5 The minimum

limit to structural si7es suggested by +arious codes and standards are usually enough to

support the weight of the building as well as the imposed dead loads and li+e loads5

owe+er& the real challenge for the structural engineer is to find out the structural

beha+ior of a building under wind and seismic actions5 The effects of these e9ternal

hori7ontal forces are highly unpredictable& and these mainly depend on building shape&

si7e& mass& floor plan layout& and climatic conditions5

;.> RESEAR#H -ROBLEM

This research aims to study the beha+ior of composite multi,storey buildings

under hori7ontal loads using belt,truss and outriggers as secondary bracings5 This topic is

analy7ed in the conte9t of a+ailable academic material and the gaps in academic research

are pointed out5 This research is targeted to fill in the deficiency of scholarly material

with respect to the thesis topic5

;.>.: -RE


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%iang et al5 '/002) studied the strength of concrete filled steel bo9 columns with a

+ariety of square and rectangular shapes& using the fibre element analysis 'where the

composite section is discreti7ed into many small regions called fibres)5

Sandun et al5 '/00@) e9plored the impact of dynamic loadings on composite floors

through finite element modeling in ABAKAS5

8llobody et al5 '/011) studied eccentrically loaded composite columns5 $oncrete

filled steel tubes were used in this research5 The authors ha+e chec!ed the strength of the

columns under +aried conditions of eccentricity and compared results with 8uro $ode 5

The performance of composite columns under high temperature was studied by

Houng et al5 '/011)5 The authors ha+e utili7ed a non,linear three,dimensional finite

element model for research using 8uro $ode 5 They ha+e used a uni+ersal column '($)

section in a reinforced concrete square column5

Academic research has limited amount of material on o+erall performance of

composite buildings& howe+erD appreciable amount of literature is present on reinforced

concrete and steel structures& such asD

Fian et al '/001) e9trapolated the efficiency of belt,truss and outriggers in

concrete high,rise buildings subjected to wind and earthqua!e loadings5 Authors used two

dimensional 0,storey model for wind and three dimensional G0,storey model for seismic

load analysis5 They came up with the optimum location of belt,truss and outriggers with

G2 and 1 lateral deflection reduction for wind and earthqua!e loadings respecti+ely5

oender!amp et al '/00E) presented a graphical method of analysis of tall

buildings frames braced with outriggers and subjected to uniform lateral loadings5

Authors ha+e used steel structures for their two dimensional model5 They ha+e concluded

that beha+ior of steel braced frame with outriggers was similar to concrete wall with

outriggers beams and further suggested that hori7ontal deflection and bending moments

were influenced by stiffness and thereforeD it should be included in the preliminary design

of tall structures 5


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oender!amp '/00C) deri+ed an analytical method for preliminary design of

outrigger braced high,rise shear walls subjected to hori7ontal loading5 e used a two

dimensional analytical model of shear wall with outriggers at two le+els& one outrigger

has a fi9ed location up the height of the structure& while the second was placed at +arious

location along the model height5 e has gi+en comparison of deflection reduction for a

/@,storey model with few combination of two outriggers floors and concluded that the

optimum location of the second outrigger was at 96 I 02CC when the first one was

placed at the top& i5e5 a6 I 005

%ee et al '/00) focused on deri+ing the equations for wall,frame structures with

outriggers under lateral loads in which the whole structure was ideali7ed as a shear,

fle9ural cantile+er and effects of shear deformation of the shear wall and fle9ural

deformation of the frame were considered5 Authors ha+e +erified the equation by

considering the concrete wall,frame building structure under uniform wind loading5

$onclusions highlighted that consideration of shear deformations of walls and fle9ural

deformations of frame in analytical formula ga+e sufficiently accurate results5

Rahgo7ar '/00@) presented mathematical model for calculation of stresses in

columns of combined framed tube& shear core and belt,truss system5 e applied his

mathematical models to E0& 0 and 20 storey buildings and compared the results with

SA- /000 software for its applicability5 e concluded with the best outrigger location at

16th and 16Gth of model height5 is study was based on pure numerical models and he

did not use the actual properties of materials i5e5 concrete or steel or composite5 e also

did not use a realistic building layout but based his finding on assumptions of certain

properties5

All the abo+e researches do not consider a comprehensi+e study of composite

structural system of dissimilar plan layouts of +aried heights with different combinationsof belt,truss and outriggers5 #ifferent combination of lateral load resisting system i5e5

single floor or double floor bracings& with +aried plan layouts and assorted heights

models would results differently5

;.>.; RE


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The history of tall buildings whether in 8urope or Asia is related to the capability

of the structure to resist wind action5

"usta+e Ale9andre 8iffel was famous for the 8iffel,type wind tunnel5 e tried to

conduct full,scale measurements of the response of the 8iffel tower under meteorological

conditions including winds at the top of the completed E00m,high 8iffel Tower& the

worlds tallest structure at that time '#a+enport& 1@C2& p5 /)5

$hen '/00) performed a frequency domain analysis of along,wind tall building

response to transient non,stationary winds based on non,stationary random +ibration

theory5

Rofail '/00) has studied +arious a+ailable techniques for dealing with building

forms in wind load scenarios5 e has conducted a few case studies of unusual structures

around the world and presented +ery useful data for engineers and researchers5

The researchers ha+e mainly focused on winds characteristics& its properties and

+ariations with respect to wind tunnel testing5 The scholarly material has a huge gap in

research about buildings o+erall beha+ior under wind loads5

;.>.> RE


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authors used static linear analysis for equi+alent static seismic loads on a E, storey

building5

The effect of component deterioration and ductile fracture on the seismic capacity

of high,rise buildings was in+estigated by %ignos et al5 '/011)5

an et al5 '/00@) has conducted sha!ing table tests on two building models of E0

stories that consisted of composite frames and R$$ shear walls5 The authors

e+aluated the beha+ior of mi9ed structures consisting of $:ST columns under +arious

earthqua!e records5

Su Q ?ong '/00C) carried out an e9perimental study on three R$$ wall

specimens to study the effects of a9ial load ratio and confinement on their performance

under artificial earthqua!e loads5

.t is obser+ed that most of the academic literature concentrates either on

indi+idual components of a structure under seismic loads or on characteristics and

properties of earthqua!e loads5 The research gap in in+estigating the o+erall ser+iceability

and durability of composite buildings under seismic loadings requires to be addressed5

;.>.? LAGS IN A#ADEMI# RESEAR#H

As discussed in sections /5E51& /5E5/ and /5E5E& although there are many research

studies and academic publications a+ailable on the composite components of buildings&

there is a scarcity of scholarly material on the o+erall beha+ior of composite buildings5

"enerali7ed theories and6or rules specific to composite buildings are scanty& while

research& tests and analytical models for indi+idual elements of composite structures are

found in abundance5 The structural designer has to go through a lengthy process of

creating a whole model with most of the details& since there are no set procedures for

finding out the requirements of outriggers and establishing the locations of these in a

building5

.t can be argued that e+ery structure is different from e+ery other& hence cannot be

related5 owe+er& when it comes to regular e+eryday buildings& this gap is particularly


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noticeable5 The procedure of optimi7ation is usually based on trial and error as well as on

past e9perience5 .f a project is delayed or cancelled& the detailed wor! that has been done

to establish the feasibility of the project could be wasted5

The aim of this thesis is to study the beha+ior of composite buildings braced with

belt,truss and outriggers under hori7ontal loadings through finite element modeling5 A

detailed parametric study has been carried out by +arying heights& plans and number and

placement of lateral bracings for commonly used building structures in .ndia5 This study

will be beneficial in the formulation of generic principals or rules for normal6usual

building structures which are co+ered by .ndian standards5 .t will also help engineers and

structural designers in their e+eryday calculations of cost and material estimation without

ha+ing to perform lengthy tas!s and putting too much energy and time into the

conceptual6primary stage of the project5

;.? ONSET OF #OM-OSITE #ONSTRU#TION

;.?.: IN#E-TION OF #OM-OSITE #ONSTRU#TION

.n the conte9t of structural engineering& the term 3composite constructionJ

designates the combined use of structural steel and reinforced concrete in such a way that

the resulting arrangement functions as a unique entity5 The goal is to accomplish a higherle+el of performance than would ha+e been the case had the two materials been used

separately5

The start of composite construction can be traced bac! about 100 years5 :rom the

time of its inception& the efficiency of composite systems has been identified as a

compelling way of augmenting structural performance5 4ore and more steel structures

are now designed compositely because of the effecti+eness of R$$ shear walls in lateral

load resistance5

Nethercot '/00& p5 1) claims that the starting period of composite construction

was 1@& when concrete encased beams were first used in a bridge in .owa and a

building in -ittsburgh5


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The initial wor! on composite construction in $anada was traced bac! to 1@// by

$hien Q Ritchie '1@@E)& when a series of tests was conducted on composite beams5

Mhong Q "oode '/001) gi+e an elaborate picture of composite construction in

$hina with a focus on the design and detailing of concrete,filled steel tube columns5

The idea of composite construction of tall tubular buildings was first concei+ed

and used by :a7lur Fhan of S!idmore& wings Q 4errill 'S4) in the 1@G0s5 This has

pa+ed the way for high,rise composite buildings li!e -etronas Towers and *in 4ao

building5 Super tall buildings such as the Burj Fhalifa& the 121 storey .ncheon Tower

under construction in South Forea& and a proposed 1 !m tower in Saudi Arabia& are all

instigated by such indigenous thoughts '4endis Q Ngo& /00& p5/)5

Taranath '/01/& p5@G) stated that apart from economy of material and speed of

construction& composite structures& due to being light weight& inflict less se+ere

foundation conditions hence results in greater cost sa+ings5

;.?.; #ASE STUDIES

8+en though there is a lac!ing of academic wor! on o+erall beha+ior of

composite buildings& there are a few case studies specific to particular buildings or

projects5

:igure /515 $apital "ate , Abu #habi


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:igure /51 shows +iew of $ity "ate tower Abu,#habi is retrie+ed from

http;66www5e,architect5co5u!6dubai6capitalgateabudhabi5htm 'e,architect& /010)5

A case study was performed on $apital "ate Tower& Abu #habi ':igure /51) by

Shofield '/01/)5 The author described that the composite structure was built with a

concrete core surrounded by steel trusses termed as 3diarigidJ5 Steel beams supported the

concrete composite floor and ran between e9ternal and internal +ertical supports5 %ateral

wind actions were counteracted by the introduction of dense outriggers at the 1Cth

mechanical floor& which connected the e9ternal frame to the central core5

:igure /5/5 Tianjin "oldin :inance 11C Tower

:igure /5/ illustrates ele+ation& brace connection and the plan of "oldin :inance

11C Tower& is retrie+ed from http;66www5s!yscrapercenter5com6tianjin6goldin,finance,

11C6CE6 'The S!yscraper $entre& n5d5)5

Tiajin "oldin :inance 11C tower ':igure /5/) was studied by -eng et al5 '/01E)5

The authors wrote that the concrete core consisted of embedded steel sections and ran

from the foundation to the top le+el5 4ega columns pro+ided at the four corners of the

building were made up of internal inter,connected steel plates enclosed by e9ternal steel


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plates& hence forming a polygonal shape5 The chambers within were filled with concrete

and reinforcement was pro+ided to satisfy a9ial& bending& buc!ling and torsional capacity5

The mega columns were connected to each other with mega braces at the structures

periphery5 The lateral load resisting system comprised transfer trusses distributed e+ery

1/ to 12 floorsD these connected the mega columns to the main core wall5 The floor

framing consist of a composite floor dec! supported by steel beams5

;.@ -ROFILED DE#9ING AS A -ERMANENT FORM

$omposite technology has a dual usage& that is& it can be used as a structural

element as well as for permanent form wor! such as profiled dec!ing5

:igure /5E5 -rofile sheeting as permanent formwor! in composite slab

:igure /5E e9emplifying profile sheeting5

Retrie+ed from http;66www5tegral5com6inde95phpUpageI$omflor 'Tegral $omflorV$omposite :looring& n5d5)5

-rofiled steel dec!ing consists of a corrugated steel sheet with an in,situ

reinforced concrete topping ':igure /5E)5 The dec!ing acts as permanent formwor! and


39/141

also pro+ides a shear bond with set concrete5 ence& when concrete gains strength& the

two materials wor! together and the profiled sheeting acts as bottom reinforcement5

This type of formwor! is e9tensi+ely used throughout the world5 .n (nited

Fingdom& 0 of +arious constructions use a composite slab system 'Nagy et al& 1@@)5

The use of a composite slab is a remar!able ad+ancement in the construction of

high,rise buildings requiring open plan space5 This has many benefits technically and

economically5

.t ser+es the following main structural purposes;

#uring the course of concreting& the metal dec!ing supports the weight of the wet

concrete and top reinforcement& together with temporary loads of construction5 The dec!ing acts Wcompositely with the concrete and ser+es as a bottom

reinforcement in resisting sagging moments of the slab as occurs with a

con+entional reinforced concrete slab5

The steel dec!ing is also used to stabili7e the beams against lateral torsional

buc!ling during construction and to stabili7e the building as a whole by acting as

a diaphragm to transfer wind loads to the walls and columns5

Robustness can be readily achie+ed by continuity between dec!ing&

reinforcement& concrete& secondary and primary elements5

The financial benefits are equally important in todays competiti+e and

enterprising construction industry5 Rac!ham et al5 '/00@& p5 /) point out the

commercial benefits of profiled metal dec!ing; speed of construction& reduced weight

of structure& easy transportation& shallow slab depth& sustainable construction and ease

of ser+ice installation5

;. O


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and double floors in different models5 The belt,truss ties the peripheral columns of the

building& while the outriggers engage them with the main or central shear wall5

Therefore& e9terior columns restrain the core wall from free rotation through the

outrigger arms5

"unel Q .lgin5 '/00C) described the outrigger system as an inno+ati+e and

efficient structural system5 The outrigger system comprises a central core& including

either braced frames or shear walls& with hori7ontal outrigger trusses or girders

connecting the core to the e9ternal columns5

:igure /55 Typical outrigger and belt,truss

:igure /5& illustrating a typical outrigger system5 Retrie+ed from online material

in http;66www5structuremag5org6article5asp9Uarticle.#IG '4elchiorre& /00)5

al '1@) studied the deflection control on a two,dimensional model with the

use of outriggers5

Fian et al5 '/001) ha+e analy7ed the efficiency of belt truss and outrigger in

concrete high rise buildings5


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Nair '1@@) suggested a concept of a 3+irtualJ outrigger system in which the

stiffness of floor diaphragms could be utili7ed to transfer moment as a hori7ontal

couple from the core to trusses or walls that are not connected directly to the core5

:igure /525 Basic +iew of& ele+ation and plan

The usefulness of belt,truss and outriggers is well,!nown& though there is always

disagreement on the reduction of operational space at the outrigger le+el5 This&

howe+er& can be curtailed by the use of diagonal cross bracing in line with thecolumns as well as the use of hori7ontal trusses that can be entrenched in a false

ceiling5 Typical outrigger arrangement is shown in :igure /525

;.C #ON#LUSION

$omposite construction is a brilliant and cost efficient solution de+eloped in this

era5 .n .ndia& structural engineers readily employ this system to sa+e time and

material5 .t is popular in office and commercial buildings5 :or sufficient stiffness and

efficient lateral load path& a system of outriggers and belt,trusses is normally coupled

with composite construction5

utriggers and belt,truss systems are in constant use in +arious high,rise

de+elopments& howe+er& their use and pro+ision is specific to a particular construction


42/141

or building structure5 (sually structural engineers ha+e to conduct a rigorous analysis

with a trial and error approach to find the number of steel braces required in a

building and their placement along the height of building5 ence& certain generic rules

and principles are needed that can help the structural designer to compute the

requirement of bracings 'i5e5 core walls& outriggers& belt,truss etc5) based on structure

height and plan dimensions 'i5e5 width and length)5 This would be helpful in the

appro9imate judgment of +arious quantities and cost 'i5e5 material& labor cost& project

time line etc5) without ha+ing to underta!e a rigorous analysis5

4oreo+er& most research has been concerned with the components of composite

structural systems of buildings& such as composite columns and composite beams5

Seismic and wind actions are also in+estigated using analytical two dimensional

models that re+ol+e around the characteristics and parametric properties5 Therefore&

this thesis aims to fill in the lac! of academic research into the o+erall beha+ior of

buildings5


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#HA-TER >

STRU#TURAL MODELING

>.: INTRODU#TION

:inite 8lement Analysis ':8A) is a numerical system for sol+ing comple9

problems5 .n this method& structural elements are di+ided into finite elements andanaly7ed for strain& stress& moments and shear etc5 :8A has been embedded in

engineering and other sciences and it is now essential in the solution of mathematical

problems5

This research is conducted by analy7ing building prototypes through :inite

8lement 4odeling ':84)5 8tabs is chosen for research because of its a+ailability in

uni+ersity and its popularity within the construction industry5

This chapter consists of descriptions of thesis models and criteria for the selection

of height and plan layouts for these models5 .t also describes the calculation of

transformed properties of composite elements& and the selection of properties for non,

composite elements5 The input of all these properties to the models and

appro9imation of models with respect to .ndian standards guidelines are e9plained5 .t

co+ers the wind and seismic loads application in models& and finally& model

+alidations are carried out to establish the prototypes reliability5

>.; ANALYTI#AL -ROGRAMME AND SOL.;.: -rogra!!esoft(are select%on


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The inno+ati+e and re+olutionary new 8TABS is the ultimate integrated software

pac!age for the structural analysis and design of buildings5 This latest 8TABS offers

unmatched E# object based on modeling and +isuali7ation tools& fast linear and

nonlinear analytical power& sophisticated and comprehensi+e design capabilities for a

wedge,range of materials& and insightful graphic displays& reports& and schematic

drawings5 $A# drawings can be directly con+erted into 8TABS models5 #esign of

steel and concrete frames& composite beams& composite columns& steel joists and

concrete and masonry shear walls& as is the capacity chec! for steel connections and

base plates5 $omprehensi+e and customi7able reports are a+ailable for all analysis

and design output& and construction drawings of framing plans& details& and cross

sections are generated for concrete and steel structures5

:igure E515 8tabs opening page

The program initiated in 1@@G already has many buildings and real life structures

in its credits& signifying the programs reliability and integrity5 :or e9ample; 3the

runner sculptureJ placed on top of Sydney towers during /000 Sydney lympics

':igure E5/)& the optimi7ation of 3?ater $ubeJ in Beijing National Aquatic $entre for


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/00 Beijing lympics ':igure E5E)& and the roof design of Terminal /8 of the

$harles de "aulle Airport in -aris& :rance ':igure E5)5

:igure E5/5 Runner sculpture& Sydney& Australia

:igure E5/5 shows Runner sculpture in Sydney& Australia is Retrie+ed from

http;66www5flic!r5com6photos6E@2211C0XN0/62C1220@GG6 'flic!r& n5d5)5

:igure E5E5 Beijing National Aquatic $entre& $hina

:igure E5E5 show an e9ternal +iew of Beijing National Aquatic $entre& $hina designedRetrie+ed from

http;66architecture5about5com6od6greatbuildings6ig6Stadium,and,Arena-ictures6?ater,

$ube5htm 'About5com Architecture& n5d5)5


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:igure E55 Terminal /8 of $harles de "aulle Airport& -aris& :rance

:igure E5 shows an e9ternal +iew of Terminal /8 of $harles de "aulle Airport& -aris&

:rance& Retrie+ed from http;66structurae5net6structures6data6inde95cfmUidIs000@/E'Structurae& n5d5)5

>.;.; SOL.;.;.: L%near stat%c sol*er

The linear static sol+er is based on the assumption that the structures beha+ior is

linear and applied forces are static5 This is based on the elastic theory& that 3element

forces are linearly proportional to element deformation and when loading is remo+ed the

element will come bac! to its original shapeJ5 Therefore& the model must follow

3oo!es %awJ5 A load is static if its magnitude and direction do not +ary with time5


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:igure E525 %inear static sol+er

4ultiple load cases are treated in one solution in this sol+er5 $ombination load

cases of primary loads are a+ailable through combining the results for primary load cases

in the post,processor without running the linear static sol+er again5 #isplacements and

results for all load combinations are calculated at the end of solution5 .n the study& this

sol+er is used for wind dynamic analysis and S analysis5

>.;.;.; Nat)ral fre)ency sol*er

:igure E5G5 Natural frequency sol+er


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The natural frequency sol+er ':igure E5G) is used to calculate the

natural6fundamental frequencies 'or free +ibration frequencies) and corresponding

+ibration modes of an un,damped structure5 The frequency sol+er offers fle9ibility in

analysis through frequency shift& mass participation and strum chec! etc5 The frequency

shift helps a+oid lower modes of +ibration and processes !ept towards the higher modes

only5 The strum chec! ensures that all the 8igen +alues ha+e been con+erged successfully

in the solution5 4ass participation is used in SS analysis5 .n the study& the frequency

sol+er is used in both wind and seismic analysis of models5

>.;.;.> S2ectral res2onse

The spectral response sol+er ':igure E5C) computes the response of a structure e9posed to

a random dynamic loading5 Two types of random dynamic loadings can be encountered;

earthqua!e base e9citation and general dynamic loads5 .n this study& earthqua!e base

e9citation is used for seismic analysis5 The spectral cur+e is defined either as 3a function

of frequencyJ or 3time period of +ibrationJ5

:igure E5C5 Spectral response sol+er

The sol+er calculates ma9imum model responses using two methods; $K$

'$omplete Kuadratic $ombination) and SRSS 'Square Root of Sum of Square)5 The

comparison of $K$ and SRSS is not the objecti+e of this study5 Based on common


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design practices& SRSS is used for model solution5 .n this study& the spectral response

sol+er is used to find out displacements under SS loading5

>.> LOADS ON MODELS

The primary loads or forces that dictate the design of most of the on,ground

structures are gra+ity& wind and earth,qua!e& although e+ery structure does not analyse or

design for all these forces5 Structural analysis of a particular structure depends upon its

location& situation& en+ironmental conditions& architectural layout& height& width& usage&

client requirements etc5 %oads acting on a multi,storey building can be broadly classified

into static and dynamic loads and their deri+ati+es& as represented by :igure E55


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:igure E55 %oads on model

>.>.: GRA


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:igure E5@5 Basic figure of gra+ity load flow

The dead loads in models comprise structural self weight& partitions& and ceilings&

air,conditioning ducts and ser+ices for office building scenarios& while li+e loads are

predominantly human loads5 The standard pro+ides certain guides for li+e loads relati+e

to occupancy5 %i+e loads used in the models are for office occupancy5

>.>.; LATERAL LOADS

The loads or forces that act perpendicular to the +ertical a9is of building are called

hori7ontal loads or lateral loads5 These loads are discussed in chapters and 25

>.? SELE#TION OF -ARAMETERS TO SATISFY THESIS

OB'E#TI.?.: AIMS

The choice of parameters integrated many factorsD the main aim has been;

To facilitate engineers in their e+eryday analysis and design wor! so that they do not


52/141

ha+e to do detailed calculations for basic structural prediction in the pre,design stages of

a project5

To study structures commonly found in the local en+ironment& for instance& local

builders prefer to construct office buildings with composite structure so that +ast&

uninterrupted rentable space can be achie+ed5

To study structures in compliance with Australian general practices and Australian

standards with the intention that e+eryday engineering wor!s can be benefitted5

To depict commonly used structural arrangement in prototypes that include floor to

floor heights& building plans and building heights etc5

To use properties of locally produced building materials and products such as floor

sheeting from %ysaght Bonde! '%ysaght Bonde!& /01/)& and steel section si7es from

Australian Steel .nstitute 'AS.& /00@) capacity tables5

To gear up the research into the structural beha+ior of composite buildings in

conjunction with the outrigger system5 :urther& to add worthwhile material that will ma!e

a significant contribution of !nowledge for incoming researchers and engineers in this

field of engineering5

>.?.; -ARAMETERS

This thesis is a comparati+e study between +arious building heights and different

plan layouts5 ence& based on the abo+e criteria and considering the local general

practice& three types of parameters are selected;

4odel heightsD

4odel plan layoutD

Belt,truss and outriggers +ariations5

>.?.;.: Mo&els he%ghts select%on

The following heights are selected based on the abo+e considerations;


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2C,storey is 1@@52 m high& gi+en the storey heights as E52m5 This is the ma9imum

allowable height as per .ndian Standards5 This is chosen to study the effects of wind and

seismic loads calculated according to .ndian standards on a ma9imum gi+en building

ele+ation5

/,storey is 1C50 m high5 This is most common type of multi,storey rise within the

.ndian urban en+ironment5 4any office and residential buildings are constructed around

this heightD hence this is an appropriate comparison with the 1@@52 m tall model5

/,storey is nearly half the height of the 2C storey model& i5e5 @ m5 This height is

selected to establish a comparison and to find out the benefits 'if any) of belt,truss and

outriggers on such a short ele+ation5

>.?.;.; Layo)t select%on for !o&els

The main object in layout selection is to allow ma9imum +ariation and maintain

distinction5 .n all models& the M,a9is represents the +ertical a9is& whereas the L,a9is and

H,a9is are planner a9es5 The plan layouts selected areD

Rectangular shape model

ctagonal shape modelD

%,shaped model5

Rectang)lar sha2e&

The rectangular ':igure E510) shape is a common shape in .ndia5 %and

demarcation is usually rectangular in most .ndia municipalitiesD therefore de+elopers tend

to go for this shape of structure5 :urther& this shape has the appeal of ha+ing windows on

both sides of the building& which yield higher rentable +alue5 The layout has higher

rigidity in one a9is and less in the otherD hence it is rele+ant to study the lateral load

effects and frequency modes of this plan layout5


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:igure E5105 Rectangular model ele+ation 'full model and shear wall)

Octagonal sha2e

This has equal plane dimensions ':igure E511) and hence can represent circular

and square buildings5 owe+erD in square shapes there are re,entrant corners that produce

swirling effects when subjected to wind actions5 Since the wind dynamic

loads are calculated according to .ndian standard& the need to counteract this effect is not

significant unless the building e9ceeds the prescribed height and wind tunnel studies

become essential5 Therefore& the octagonal shape can stand for the square shape5

:igure E5115 ctagonal model ele+ation 'full model and shear wall)


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L,sha2e& !o&el

This is selected to study an e9tended layout with double core walls in both of its

arms ':igure E51/)5 .t is more massi+e than the other two shapes5 The effects of lateral

loads on this model are studied and compared with the other two less rigid models5 The

corner wall around the stair well and side walls are needed to stabili7e the model and

achie+e the desired frequency mode shapes5

:igure E51/5 %,Shaped model ele+ation 'full model and shear wall)

>.?.;.> O)tr%ggers 2ro*%s%on %n !o&els

Belt,truss and outriggers are used as secondary bracings for lateral load resistance

in conjunction with a primary bracing& that is& an R$$ shear wall5 The studys main focus

is the utili7ation of belt,truss and outriggers in +arious ways in models and analysis of

their outcomes5 4any shapes of truss system are a+ailable in the mar!etD howe+er& the

crucial objecti+e of this study is not the shape of the truss but its location5 Therefore& a


56/141

commonly used system of cross,bracing is adopted& as shown in :igure E51E5

:igure E51E5 utriggers and belt truss

The desirable structural system is one which has least obstructions& that is& fewercolumns and outrigger le+els and more rentable space5 The floors with outriggers are

mainly used for storage or as electrical and6or mechanical equipment roomsD hence they

are usually not rentable and not desirable5 Therefore& models are tried starting with one

belt,truss and outriggers up to four truss le+els5 These le+els are split along the height in a

+ariety of double floor outriggers and single floor outriggers5 The placement of truss


57/141

le+els are finali7ed based on the most effecti+e places along the height of +arious models5

These arrangements are !ept the same in Rectangular& ctagonal and %,shaped models

'Table E51)5

Table E51

4odel arrangements

>.@ STRU#TURAL SETU- OF MODELS

To achie+e the thesis objecti+es& finite element modeling of building prototypes is

carried out within the limitations and scope of .ndian standards5 -rototypes are modeled

as braced frame structures& i5e5 additional structural elements are pro+ided to resist lateral


58/141

loads5 These bracings are classified as primary bracings 'i5e5 R$$ shear walls) and

secondary bracings 'i5e5 belt,truss and outriggers)

Belt,trusses engage peripheral columns and outriggers connect these columns to

R$$ shear walls5 Thus& hori7ontal loads on the structure get transferred from e9ternal

columns to shear walls& which carry them to the foundation5

%i et al5 '/010& p5 1) has emphasi7ed that in steel,concrete hybrid structures&

reinforced concrete shear walls with high lateral stiffness are usually selected to

confront hori7ontal loads originated by winds or earthqua!es& while steel frames with

greater strength are generally designed to sustain the +ertical loads5 .n addition& hybrid

structures can easily be tailored to large,span architectural spaceD therefore& they are

particularly attracti+e to real estate de+elopers5 The elements used in prototypes are gi+en

in Table E5/5

Table E5/5

4odels structural arrangement

>.@.: -ROTOTY-E SET,U- IN Eta6s

$omposite structural elements consist of slab and columns ':igure E51)5 $entralcore and side walls are R$$ shear walls5 -rimary beams& secondary beams and belt,truss

and outriggers are structural steel sections5 .n 8tabs models columns& beams& belt,truss

and outriggers are modeled as beam elements5 -late elements are assigned to composite

slab and shear walls5


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:igure E515 Slab and column composite sections

:igure E51 shows a section of composite slab and column& adopted from online material

in http;66www5steelconstruction5info6$ompositeconstruction 'Steel$onstruction5info&

n5d5)5>.@.:.: #onstr)ct%on ty2e

Simple construction is adopted for models based on the definition pro+ided in

.ndian Standard5 enceforth& rotation end releases are assigned to both ends of all


60/141

primary and secondary beams to depict pin connections ':igure E512)5

:igure E5125 Beam& column and shear wall arrangement and beam end releases

>.@.:.;


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:igure E51G5 Support6restraints at base

>.@.; TRANSFORMED -RO-ERTIES FOR #OM-OSITE ELEMENTS

8qui+alent transformed properties of slab and columns are used in three

dimensional models to mimic the ma9imum realistic beha+ior of buildings under

dynamic wind and seismic loads5

4odulus of 8lasticity $E) of composite elements are used to) and #ensity5

$alculations of these properties are shown in Appendi9 A5 $omposite mass contribution

is included through density5

:or instance& the density of the R$$ column is /200 !g6mED howe+erD with

embedded .,section& the combined density becomes /G00 !g6mE ':igure E51C)5 Similarly&

the elastic modulus of 1004-a concrete is //00500 4-a and of structural steel is

/00&000500 4-a5

The combined elastic modulus of composite column is higher than concrete and

lower than a steel elastic modulus ':igure E51C)5


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The transformed elastic modulus of composite section is gi+en by 8quation

ACEC+ASTE S=AgET E5E

The transformed density of the composite section is gi+en by 8quation E5;

ACC+ASTS=Ag T E5

?here;

AgI "ross area of section

AcI Area of concrete

ASTI Area of steel

8cI 8lastic modulus of concrete

8sI 8lastic modulus of steel

8TI 8lastic modulus of transformed section

cI #ensity of concrete

sI #ensity of steel

TI #ensity of transformed section


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:igure E51C5 Abstract from composite column spread sheet

>.@.;.: #o!2os%te col)!n

:or the composite column& +arious .,sections are selected from the #esign

$apacity Table for Structural Steel5 .n addition to .,sections& +ertical bars along column

edges6sides are included in the column capacity calculations5 The steel to concrete ratio is

!ept well below Ag to accommodate lateral restraints& that is& stirrups5

$olumns are di+ided into two main categories; internal columns with a load

catchment area of 100 m/6floor and edge columns with a load catchment area of 20 m/

6floor5 The transformed properties of columns are summari7ed for / storeys& / storeys

and 2C,storey in Table E5E& Table E5 and Table E52 respecti+ely5

The si7es of columns are based on gra+ity loadsD therefore a higher le+el column

has a smaller cross,sectional area5 .n a /,storey building& the ma9imum column si7e is

20 mm/ 'Table E5E)& whereas in a 2C,storey building 'Table E52) the ma9imum column

si7e is 1/20 mm/5


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Table E5E

$olumn si7es of / storeys '@50 m)

Y9,area Icross,sectional area of column in mm/

Table E5

$olumn si7es of / storeys '1C50 m)


Table E52

$olumn si7es of 2C,storeys '1@@520 m)


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>.@.;.; #o!2os%te sla6

$omposite slabs consist of corrugated profiled sheeting with concrete topping

':igure E51)5 The o+erall depth of slab is selected as 1/0 mm '%ysaght Bonde!& /01/)

for a /52m span length5 The cross,sectional area& steel modulus and density of sheeting

are e9tracted from Bonde!s manual '%ysaght Bonde!& /01/)5 The spread sheet is

formulated and formulas are entered to calculate composite slab properties ':igure E51)5

:loor loads are !ept the same throughout the building because the main focus of the

thesis is to study models under lateral loads for ser+iceability5


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:igure E515 $omposite slab 'abstract from Appendi9 $)

>.@.> #ORE =ALLSHEAR =ALL ARRANGEMENTS5

4odel plans must satisfy .S $odes in order to achie+e the thesis objecti+es5 The

process of complying with .ndian standards is tedious and repetiti+e and in+ol+ed many

3model runsJ and 3re,runsJ& to;

Satisfy minimum thic!ness for :R% ':ire Rating le+el)D

$omply with the access and egress requirementsD

Attain certain shear wall arrangements so the first two natural frequency modes

represent the translational modes of structural +ibrations5

The first two goals are achie+ed by placing the lift shaft and stairs at appropriate

positions in the layout5 Natural frequency mode shapes of building are go+erned by the

core wall position in the layout& whereas the +alues of natural frequencies are controlled

by wall thic!nesses5 .ncreasing wall thic!nesses does not help to change mode shapes5

Therefore& the shear wall position in the layout is adjusted and readjusted to achie+e

required mode shapes5


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The final shear wall arrangement around the lift core is shown in :igure E51@5 The %,

shaped layout has two core walls around two lift shafts placed at two arms of the

building& while the rectangular and octagonal layouts are pro+ided with one lift shaft in

the centre5

:igure E51@5 $ore layouts

>.@.? STRU#TURAL STEEL ELEMENTS

Steel sections are pro+ided for main 'primary) beams& secondary beams and steel

bracing members 'belt,truss and outriggers)5 Secondary beams are typically 10 m spanswith /52 m centre to centre distance& and are supported on main6primary beams5

4ain6primary beams are pro+ided at 10 m spacing and typically span 10 m5 These

sections are selected based on the neSteel guidelines and are listed in -roperties of these

sections are directly input from 8tabs build,in library of programme5 Table E5G5 -roperties

of these sections are directly input from 8tabs build,in library of programme5

Table E5G

Structural steel section in models

Bea! Sect%ons

4ain6primary beam '-B1) E00YE00mm

4ain6primary beam '-B/) > 10 m span G00YG00mm


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Secondary beam G00YG00mm

>. ANALYSIS OF RESULTS

Analysis of wind and seismic effects show deflection& storey drift and natural

frequencies5 #ynamic effects are injected in the lateral loads calculations through natural

frequency5

Deflect%on $ + or displacement is the de+iation of the whole structure or

structural element from its neutral position under an applied load and is measured in

3mmJ5

Storey Dr%ft $+ or inter,storey displacement is the lateral drift of a le+el relati+e

to the le+el below in a multistorey structure and is measured in 3mmJ5

Fre)ency $f+ is the oscillation of any object about its neutral 'central) position5

.n structural engineering the number of complete cycles of the to,and,fro motion of a

building about its neutral a9is is called its frequency5 :requency is a reciprocal of the time

period& i5e5 f I 16T and is measured in 37J5

>.C O-TIMISATION -RO#EDURE

To achie+e a structural arrangement that satisfies frequency criteria and

deflection limits of the rele+ant standards is a repetiti+e tas! and a 3trial and errorJ

procedure5 *ayachandran 'p5 2& /00@) wrote that o+erall optimi7ation of a tall building

frame has been comple9 and time consuming5 To comply with .ndian standards& models

are optimi7ed for wind and seismic analyses5 Some of the optimi7ation steps are common

for both loadingsD these are;

.nput of minimum prescribed wall thic!ness& column si7es and slab and beam properties

for first run of modelD

Self,weight reactions and model mass are e9tracted from the programme and compared

with manually calculated +alues as an initial model +alidity chec!D


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The first run is 3natural frequency analysisJ that gi+es the fundamental frequency of

+ibration of a structure5 4odels are run and re,run many times5 :or each sol+er cycle&

shear wall positions and thic!nesses are adjusted until the desired mode shapes are

achie+ed5

=%n& analys%s

.n addition to the abo+e steps& optimi7ation for wind analysis includes the

following;

Acquired frequency is used to calculate dynamic cyclonic wind loads& which consist of

along,wind and crosswind responsesD

Along,wind and crosswind responses are then applied in the directions of first mode

and second mode of frequency respecti+ely in the model 8tabsD

.ndian Standards ad+ocate using along,wind and crosswind responses simultaneously

on a structure5 %oad combinations for these are gi+en in Table E5C5

Table E5C

?ind load cases

Loa& #o!6%nat%ons#ases : ;

Along Z wind 'H,a9is) 1 05E

$rosswind 'L,a9is) 05E 1

Se%s!%c analys%s

The steps for earthqua!e analysis are followed after the common steps5 The load

combination in Table E5 is common for S and SS loadings5

Table E5

Seismic load cases


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ori7ontal design response spectrum analysis 'S)

The S analysis is performed as;

The frequency for the first mode of +ibration is used to calculate hori7ontal design

action coefficient '$d'T)D

:actor ') for S load is then calculated as gi+en in 8tabs ?eb notes '/011) as in

8quation E52;

=[kpZCh(T1)Sp

] E52

This is used to generate hori7ontal shear in L and H directions based on structural self,

weight and non,structural mass already pro+ided during modeling5

Site,specific design response spectra analysis 'SS)

The calculation of SS analysis is based on two +ariables& i5e5 3site sub,soil profileJ

'gi+en in chapter 2) and 3modal mass participationJD

4odal mass is obtained by natural frequency analysis5 The model is run up to ten

frequency modes to achie+e desirable mass participation5

Site,soil profile is gi+en by the normali7ed response spectra in the form of a graph&

further described in chapter 25

The factor for SS loading is gi+en in web note 'StrandC ?eb notes& /011) as in 8quation

E5G;


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Factor=[kpZxSp

] E5G

The abo+e +alues are then input in 8tabs for SS analysis5

>. MODELLING


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Base Shear , crosswind '!N) GE@2 C11/G 105CE

Base Shear hori7ontal design response spectrum 1/E0 1/@@ 25E11

+erturning moment, hori7ontal design

response spectrum @1E@ @/@@E 15GC/

?;,Storey L, Sha2e& !o&el $:?C. !+

.n Table E510& base shear due to along,wind and crosswind responses ha+e the

highest differences5 4anually calculated +alues are higher because linear force cannot be

assigned to the entire length due to the presence of R$$ walls around the stair well 'at

the corners)& whereas total length and width are considered in manual calculations5 Het

the difference is within acceptable limits of 2 to 10 as an adopted general practice of

+alidation5

Table E510

Summary of modeling +alidation for , Storey %, Shaped model '1C50 m)

Ite!s Man)al #als Eta6s D%fference

89terior column load '!N) E12 EGE 052C

.nterior column load '!N) 1G@/@ 1GGE1 15C@/

Base shear Z along,wind response '!N) /0G/G1 /1CC0 25E0

Base Shear , crosswind '!N) 1@EE0 1/1E0 50E

Base Shear Z hori7ontal design response spectrum 11/1 11/1 05001

+erturning moment, hori7ontal design response spectrum 1/11 1/EC 05/EG

@C, Storey rectang)lar !o&el $:.@ !+

All the +alues in the rectangular model& as gi+en in Table E511& are +ery close and

the differences are minimal5 The base shear of the along,wind response has the highest


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percentage of difference among all the comparisons in Table E511& while the base shear

due to S loads has the least difference5

Table E511

Summary of modeling +alidation for 2C, Storey rectangular model '1@@520 m)

Ite!s Man)al #als Eta6s D%fference

89terior column load '!N) 11G0@ 111G 15GG

.nterior column load '!N) //2@ /EC@ 052

Base shear Z along,wind response '!N) E@@@0 //EE /5G2

Base Shear , crosswind '!N) EC210/@ EC2G0 0512

Base Shear Z hori7ontal design response spectrum 1E01 1E01 05001

+erturning moment, hori7ontal design response spectrum 1GC02 1GEG 051/

#ifference I ['4anual load Z 8tabs output)6 4anual %oad\ 9 100

>. #ON#LUSION

The chapter has presented successful& stable and robust models of 8tabs5 The

process in+ol+ed calculations of transformed properties of slab and column and their

application in :845 The optimi7ation of shear walls was carried out to achie+e desired

mode shapes for fundamental frequency5 Robustness of the model was ascertained

through comparison of +arious manually calculated and programme,generated outputs5

The +alidation percentages were within the acceptable limits of 2,10& which was also

indicati+e of correct input parameters in the models5


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#HA-TER ?

=IND A#TIONS ON BUILDINGS

?.: INTRODU#TION

This chapter outlines the deri+ation& orientation and application of wind actions

on office prototypes de+eloped in finite element software '8tabs)5 These forces aredefined and their computation is carried out with respect to .ndian Standard5 Selection of

+arious +ariables and multipliers is performed with regard to the thesis topic and their

choice is then justified5 The application of wind linear force in :84 is gi+en in detail5

The results contained in this chapter pro+ide comparison between deflections and

frequencies of +arious models5 Altogether& fifty se+en,models are run5

The three plan layouts 'i5e5 Rectangular& ctagonal and %,shaped) are analy7ed

and studied for three different heights 'i5e5 @m& 1Cm and 1@@52m)5 All these models are

sol+ed for a +ariety of belt,truss and outrigger options5 :indings and irregular trends are

discussed with the help of graphs and tables5 The conclusion and results are presented at

the end of chapter5 .n the following paragraphs& the terms 3trussJ and 3outriggersJ will be

used interchangeably and these ha+e the same meanings i5e5 3belt,truss and outriggersJ5

?.; =IND

?ind is perceptible natural mo+ement of airD its flow can be sua+e li!e a 7ephyr

or can be hapha7ard and tempestuous5 Structural engineering translates wind as a natural

phenomenon that puts forward an obtrusi+e force on buildings5 Taranath '/010& p5 /22)

states that wind is the term used for air in motion and is usually applied to the natural

hori7ontal motion of the atmosphere5 Air flow is three,dimensionalD it has one +ertical

and two hori7ontal components5 .n multi,storey building design& +ertical air flow is of


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less significance than hori7ontal air flow5 The +ertical air pressure is counteracted by the

weight of a building and hence is not a peril5 Therefore& the terms wind action& wind

force& wind load& wind speed& wind +elocity and wind pressure all correspond to the

hori7ontal component of air flow5

?.> AIM AND S#O-E OF MODELLING FOR =IND LOAD

ANALYSIS

?.>.: AIMS

?ind actions are calculated according to the guidelines of wind standard

To assist ci+il6structural engineers in .ndiaD

To add useful and +aluable research material to the selected topicD

To offer new directions in research to upcoming scientist and researchers5

?.>.; S#O-E

-rinciples and statistics pro+ided in .ndian Standards are based on wind tunnel

testing& field measurements of +arious locations in .ndia and established fluid mechanics

rules5 The methods and procedures outlined in the standard are sufficient to achie+e

realistic wind actions in standard situations5 owe+er& there are certain limitations

relating to structural height and fundamental frequency5 .n addition& structures li!e lattice

towers& offshore structures and bridges are outside the scope of the wind standard5

?.>.> #OM-LIAN#E =ITH =IND STANDARDS

Three different plans 'chapter E) rectangular& octagonal and %,shaped are

generated for the ma9imum height of 1@@52 m 'i5e5 2C,storeys) which satisfies the

requirement of clause 151 of the standard5 -lan dimensions of the rectangular model are

E0 m and 0 m ':igure 51)D plan dimensions of the %,shaped model are G0m and 0 m

':igure 5/)D and plan dimensions of the octagonal model are G0 m in each direction

':igure 5E)D these are also in compliance with it is only applicable for a frequency range


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of 05/7 to 15075 The frequency is directly related to structural stiffness& as gi+en in

equation 51;

fn=1

2k

m

Hz 51

ereD

fn I natural6fundamental frequency

! I stiffness 'N6m)

m I mass '!g) I E5112@/G2E2@

.f mass is !ept constant than frequency is directly proportional to the square root

of stiffness5 ence& the higher the stiffness the greater would be the frequency5

:igure 515 :orce on rectangular layout


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:igure 5/5 :orce on %,shaped layout


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:igure 5E5 :orce on octagonal layout

?.? DETERMINATION OF =IND A#TION TY-E

?ind actions on any structure or structural component can be 3staticJ or

3dynamicJ as classified by standard5 The decision as to the type of actions to be applied

on any structure or structural component depends on +ariables such as frequency&

dimensions and location5 A steady flow of wind e9erts 3static forcesJ while turbulent

wind applies 3dynamic forcesJ to structures5 ?hen a wind gust touches its ma9imum

+alue and dies out in a time much longer than the +ibration period of the building& the

wind action is considered as static5 ?hereas if a wind gust attains its pea! +alue and dies

down in a shorter time than the period of the building& its effects are dynamic5 As per .S&

if a structure has a frequency more than 1 7 then it is analy7ed and designed for static

wind loads5 Stoc!y structures fall in this category& while lean or tall structures usually


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ha+e frequencies less than 175 ence in tall structures& dynamic loadings imposed by

the wind are critical5 The models in this study ha+e a frequency below 1 7& therefore

dynamic wind loads are applied in :845

?.@ #HOI#E AND #AL#ULATIONS OF =IND


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?est to North5 Then this region e9tends towards the east5 ?ith the escalating

metallurgical and mining industry& the areas co+ered by region $ are becoming ebullient

and animated5 The municipalities near the coast in region $ are frequented by substantial

passers,by as well as long term settlers5 -rogression and e9pansion is underway with the

emergence of city centres& shopping malls& hospitals& recreational facilities and amenity

yards5 These could be the future cities of .ndia with high,rise and multi,storeys5 .n short&

Region $ not only represents cyclonic wind actions but also e9tends to a larger part of

coastline co+ering prospecti+e cities with the potential of changing into metropolises5

?ind forces are calculated in concurrence to region $ specifications of .ndian standards

and applied to commonly use office building prototypes5

:igure 525 ?ind Regions of .ndia


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?.C A--LI#ATION OF =IND LOADS ON MODELS

The most popular way to apply wind loads on finite element models is as a linear

force on elements or members5 The general equation of calculating p7 'wind pressure

normal to surface in !N6m/) is gi+en in equation 5C5

Pz=0.000683(Vzmzcat)2KN

m2 5C

The number 05000GE represents wind multipliers& as e9plained in section 52&

and e+aluated in Appendi9 B5 The only +ariable in equation 5C is 47&cat 5 The 3p7J is

multiplied by a half storey height abo+e and a half storey height below to get the linear

pressure in !N6m on a particular le+el ':igure 5)5 This pressure is then applied to

hori7ontal beam members in 8tabs in the appropriate direction5 The application of

pressure using this approach is less complicated and chec!s could be performed with

certainty5

:igure 55 %inear wind pressure on :84 4odel


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?. =IND LOAD IN-UT IN MODELS

8tabs pro+ides the facility of force pro+ision in local a9es 'i5e5 9& y and 7) and global a9es

'L& H and M) ':igure 5@)5

:igure 5@5 Application of wind on model in 8tabs

?ind action is considered a global phenomenon that is& acting on the o+erall

structure& because the target is to e9amine the o+erall structural ser+iceability

performance5 Therefore& these forces are applied as 3"lobal -ressureJ in !N6m by

selecting hori7ontal beam members on each le+el in H,dir5 and L,dir5 for along,wind and

crosswind pressure respecti+ely ':igure 510)5 %inear wind force along the ]+e H,a9is of

the rectangular 'partial) model is applied on edge beams as shown in :igure 5105 These

edge beams are designated as main beams in the model5


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:igure 5105 Along,wind linear force on Rectangular 4odel 'partial model)


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Analysis of three model types through 3Natural :requencyJ sol+er5

The first two linear modes are established5 The third torsional mode is not used in this

study5

The two linear modes are then used in an 89cel sheet to calculate along wind and

crosswind actions on office prototypes5

Thereafter these forces are applied to the model with gra+ity loads5

:inally the models are run through 3%inear StaticJ sol+er to attain results5 These models

are& howe+er& sol+ed for many belt,truss and outrigger options as listed in Table E5/&

Table 5/and Table 5E5 :or each plan layout& nineteen models are run& which amounts to

fifty,se+en models altogether5

?..; Mo&el o)t2)t

To perform the ser+iceability performance re+iew of the models +alues of

frequency& deflections and storey drifts in L,dir5 and H,dir5 are e9tracted from the analysis

results and listed in Table E5/& Table 5/ and Table 5E5


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Table 51

Results for rectangular models


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Table 5/

Results for ctagonal models


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Table 5E

Results for %,shaped models

?.: #OM-ARISON AND DIS#USSION OF OUT-UT

?.:.: STIFFNESS RATIOS


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The +alues in are calculated according to the basic equation of linear stiffness for

each model5 8lastic linear stiffness is a characteristic of elastic modulus& area and length

and is gi+en in equation 5@;

k=AEH

Nm 5@

! I stiffness

A I area in m2

I building height in m

8 I elastic modulus in 4-a

RatioA and Ratio B are calculated by !eeping 8 as constant& is the total height of

structure in meters and A is the plan area of layout in m/& henceD

!A

H

?hereD A I b 9 d& then

'! b 9 d)6

Thus& for each directionD

RatioA ! b6 and RatioB !

d6

:or Ratio $& the plan dimensions are replaced by the combined cross,sectional area of

core walls and side walls '

i Optimisation of Lateral Load

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