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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
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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
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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
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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$$ shear wall5 The studys main focus
is the utili7ation of belt,truss and outriggers in +arious ways in models and analysis of
their outcomes5 4any shapes of truss system are a+ailable in the mar!etD howe+er& the
crucial objecti+e of this study is not the shape of the truss but its location5 Therefore& a
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commonly used system of cross,bracing is adopted& as shown in :igure E51E5
:igure E51E5 utriggers and belt truss
The desirable structural system is one which has least obstructions& that is& fewercolumns and outrigger le+els and more rentable space5 The floors with outriggers are
mainly used for storage or as electrical and6or mechanical equipment roomsD hence they
are usually not rentable and not desirable5 Therefore& models are tried starting with one
belt,truss and outriggers up to four truss le+els5 These le+els are split along the height in a
+ariety of double floor outriggers and single floor outriggers5 The placement of truss
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le+els are finali7ed based on the most effecti+e places along the height of +arious models5
These arrangements are !ept the same in Rectangular& ctagonal and %,shaped models
'Table E51)5
Table E51
4odel arrangements
>.@ STRU#TURAL SETU- OF MODELS
To achie+e the thesis objecti+es& finite element modeling of building prototypes is
carried out within the limitations and scope of .ndian standards5 -rototypes are modeled
as braced frame structures& i5e5 additional structural elements are pro+ided to resist lateral
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loads5 These bracings are classified as primary bracings 'i5e5 R$$ 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
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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)
Y9,area Icross,sectional area of column in mm/
Table E52
$olumn si7es of 2C,storeys '1@@520 m)
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Y9,area Icross,sectional area of column in mm/
>.@.;.; #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 '
Recommended