Dynamic Wind Analysis of High-Rise Building
Kale Shivani Rajendra
1 , Dr. Y. M.
Ghugal2
1PG Student, Government college of Engineering, Karad, Maharashtra, 415124, India
2 Professor, Government college of Engineering, karad, Maharashtra, 415124, India
***
Abstract - Due to extensive urbanization, high-rise construction is a new trend in Indian metropolitan areas. High-rise buildings have distinct design requirements than low- and mid-rise structures. Typically, the wind is the critical load that must be taken into account in tall buildings for the structure's safety and serviceability. Due to along-wind and across-wind, any tall building may shake and oscillate in both directions. Even though the structural damage is not imminent, these oscillations could nonetheless be uncomfortable for the occupants. As a result, serviceability requires a precise measurement of building motion. Both the national building code and other Indian standard codes fall short in addressing the various problems associated with towering buildings. BIS just published the Code IS 16700: 2017 “Criteria for Structural Safety of Tall Concrete Buildings”. This Work deals with the detailed wind analysis of 180m tall building as per IS 16700: 2017.
Key Words: High-Rise, wind, along, across, oscillationsetc
1. INTRODUCTION
Thewind-inducedresponseofatallbuildingdependsonavarietyoffactors. Theseincludethebuilding'sgeometricaland dynamical characteristics as well as the approach flow's turbulence characteristics. There are a few analytical methods availableforcalculatingthewind-inducedresponseoftallbuildingsinbothalongandacrosswinddirections.Aerodynamic forces,suchasthedragforceandliftforce,actonstructuresundertheinfluenceofwindflow.Thereisadragforceacting paralleltothemeanwindandaliftforceactingperpendiculartothatforce.
2. METHODOLOGY
Methodologythatwillbeadoptedisasfollows,
1. Carryoutliteraturereviewtounderstandthetallbuildingdesignphilosophy.
2. AnalyticalEstimationoftheDynamicWindResponseasperIS875:2015(part3)
3. StudyofGustfactormethodwhichisperformedonsingletowerwith54floors+terracehavinganapproximateheightof 180m.
4. TheModellingwillbedoneinETABS.
Model
StructurewithDynamicwindloadingaspercode.
5. AnalyzetheResultobtained.
2.1 PARAMETER CONSIDERED FOR ANALYSIS
Theloadalongwindordragloadiscalculatedusingthegustfactorapproach.TheCodeIS875:2015providesthe"gustfactor method,"butthesemethodsforcomputingloadalongwind,acrosswind,orforothercomponentsarenotyetfullydeveloped. forallbuildingkinds.However,adesignerispermittedtocalculateallwindspeedsusingthegustfactorapproach.Elementsof loadonastructureutilizinganytheorythatisaccessible.Asaresult,thefollowingfactorsaretakeninto:
2.2 DESIGN WIND SPEED AND WIND PRESSURE
Togetdesignwindvelocityateveryheight(Vz)fortheselectedstructure,thebasicwindspeed(Vz)foranylocationmust beobtainedfromFig.1IS:(875(Part3)-1987)andadjustedtoincludethefollowingeffects:
Vz=Vb.k1.k2.k3
Thefollowingconnectionbetweenwindpressureandwindvelocityshallbeusedtodeterminethedesignwindpressure atanyheightabovemeanlevel:
Pz=0.6(Vz)^2
2.3 Wind load calculation as per IS 875 (part 3):2015
Thevariationofwindforceonastructuremustbeknownforthepreliminarydesign,whichincludestheproportioningofthe structure.Themeteorologicaldepartments'extensivedataonwindspeedsandthefindingsofresearchdonetocomprehend wind features and their impact on structures, based on these data and experiments conducted in wind tunnels, form the foundationofthewindloadingcodes.Dependingonthekindofbuildingorstructure,theIS875(Part3):2015suggestsusing eithertheforcecoefficientapproachorthegustfactormethodforthecomputationofwindloads.So,inordertocalculatethe windload,dynamicanalysismustbedoneiftheaspectratio,ortheheighttominimumlateraldimensionratio,ismorethan5 orthenaturalfrequency.lessthan1.0ispresentinthefirstmode.Thecodeadvisestakingintoconsiderationaninterference factor (IF) as a multiplication factor for the wind loads corresponding to isolated buildings in order to account for the interferenceeffectofanotherinterferingtall buildingofthesameordifferentheight,basedonstudiesontallrectangular buildings. According to the code, the interference zones have been divided into four zones based on the distance to the interferingstructure'sposition.
Along wind load
Tallbuildingsareconsideredflexibleslenderstructures,andIS875(Part3):2015definesagustfactororgusteffectiveness factor technique for determining along wind load or drag load. The process calculates the Gust Factor using hourly mean windspeed.Thedesignpeakalongwindbasebendingmomentwascalculatedbyaddingthemomentsbroughtonbydesign peakalongwindloadsactingalongthebuilding'sheightatvariousheightsasfollows::
Ma=Σ FzZ
Thealongwindloadonastructureonastripareaatanyheightz(m)isgivenby:
whereCf,zisthedragforcecoefficientforthebuildingcorrespondingtoAz,Azistheeffectivefrontalareaconsideredfor thestructureatheightzinPd, isthedesignhourlymeanwindpressureatheightzduetohourlymeanwindandGisthe gustfactor.
Across wind load
AnempiricalformulaproposedbyIS875(Part3):2015issuggestedfortakingintoaccountthedynamicimpactsofacross windloadflexibleconstructions.Forenclosedbuildings,thecrosswisewinddesignpeakbasebendingmomentMcis providedby:
Mc=0.5ghphbh^2(1.06-0.06k)√(
Wheregh= √2loge (3600fa), apeakfactorincrosswinddirectionforresonantresponse,Phishourlymeanwindpressureat Heighth(Pa),kisamodeshapepowerexponentforrepresentationofthefundamentalmodeshapeandCfsisacrosswind Forcespectrumcoefficientgeneralizedforalinearmode. Then,theacrosswindloaddistributiononthebuildingobtainedfromMcusinglineardistributionofloadsas:
Fzc=(3Mc/h^2)*z/h
Table -4 Alongwindandacrosswindcalculationusinggustfactormethod
Alongwindandacrosswind
3. RESULT
ResultsobtainedfromtheanalysisoftheEtabsmodelsusingabovevalueareasfollows:
BaseShearResults:
BaseshearinX–directionbydynamicwindanalysismodelisfoundouttobe45500kN
BaseshearinY–directionbydynamicwindanalysismodelisfoundouttobe24661kN
DeflectionResults:
DeflectioninX
directionbydynamicwindanalysismodelisfoundouttobe322.29mm
DeflectioninY–directionbydynamicwindanalysismodelisfoundouttobe255.03mm
DriftResults:
DriftinX–directionbydynamicwindanalysismodelisfoundouttobe0.00228
DriftinY–directionbydynamicwindanalysismodelisfoundouttobe0.001787
4. CONCLUSIONS
1. Thegust effectivenessfactorapproachprovidescritical windpressurestobetakeninto considerationinthe designof multistoryframesbecausethegustpressurescomputedbythismethodrisewiththeheightofthebuildingandaremore importantthanstaticpressures.
2.Theenergycontentofthewind'schangingcomponentalsorisesasbuildingframeheightdoes.
5 SCOPE FOR FUTURE WORK
1.Tallbuildingswithvariedaspectratiosandvariousaerodynamicmodificationsexhibitvariouswind-inducedresponses alongandacrossthem.
2.Alongandacrosswind-inducedreactionsoftallbuildingswithvariousstructuralsystemsandaspectratios.
6. REFERENCES
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[7] Pooja Niphade, Prof.Amruta.G.Whatte.“Gust Analysis of Tall Building by IS 875(Part3)-1987 and by ETabs software “,IJESTERVol5.No.3(2018)
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[9]ReviewofIndianWindCode–IS–875(part3)1987DocumentNo.IITK–GSDMA–Wind 01 –V 2.0, IITK –GSDMA Project on Building Codes, Department of CivilEngineering,IITKanpur,India(2004)
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