International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1447 Performance based seismic evaluation of G+2 RC building with varying central opening in infill walls. Renu Dambal1, Basavaraj Gudadappanavar2 1 Mtech, CAD Structural-Civil Engineering Department, SDMCET Dharwad, Karnataka, India 2 Asst. Professor Civil Engineering Department, SDMCET Dharwad, Karnataka, India ---------------------------------------------------------------------***---------------------------------------------------------------------Abstract-Inthemultistorybuildingsthemasonry infillwallswillbeadvantageousforresistingthe lateralforcesduringearthquake.Thelateralforce resistanceofthebuildingisreducedbyprovidingthe openingsintheinfillwallstheopeningsmaybeinthe formofwindows,doorsetcwhich areunavoidable.The presentpaperstudiestheperformancebasedseismic weaknessoftheG+2threedimensionalreinforced multistoreybuildingmodel,withdifferentpercentage ofopeningsatcenterinunreinforcedmasonryinfill wallsrangingfrom10to35%.Thebuildingmodels which are taken into account are bare frame, full closed frameandunreinforcedmasonryinfillwallsare modeledbyprovidingequivalentdiagonalstrutwith pinjointed.Seismicanalysisforloadcombination 1.2(DL+LL+EL)forseismiczoneIIIiscarriedoutfor three storeyed building. The present paper also present theperformancebasedseismicevaluationusing nonlinear static push over analysis. The results natural period,lateraldisplacement,storeydrift,baseshear, areobtainedandcomparedfordifferentsixbuilding models.TheanalysisiscarriedoutusingETABS nonlinearversion9.1.1.Theresultsobtainedfor different loadingconditionsforthreestoreyedbuilding showedthatthenon-ductileRCmultistoreybuilding withcentralopeninggreaterthan30%,inthe unreinforcedmasonryinfillwallsaremoreweak,and when the central openings is more than 40% the lateral stiffness should not be taken into consideration. Key Words: Infill wall, Base shear, Performance point Drift, Displacement. 1. Introduction Analysisofthebuildingdamagefromstrongearthquake revealsmanyinstancesinwhichthepresenceofmasonry infillhasadvantageouslyaffectedthelateralresistanceof reinforcedconcretemultistoriedstructure.Althoughthe infillpanelsignificantlyimprovesbothstiffnessand strengthofthestructure,buttheroleoftheseinfillpanel isnotconsideredintoaccountbecauseofdeficient knowledge of combined behavior of frame and infill. Eventhoughtheinfillwallsincreasesthelateral strengthofthestructureitisunavoidabletoprovidethe openingsintheinfillwallswhichreducethelateral strength of the structure. Further provision of openings in thewallsofthesoftstoreybuildingprovestobecritical condition.Reductionofthelateralstrengthofthe structureduetothepresenceoftheopeningsintheinfill walls depends upon the various factors such as percentage of opening,aspectratio andthelocationof theopeningin themasonrywall.Analysisanddesignofthestructure withoutconsideringthereductionofthelateralstrength duetothepresenceofopeningsintheinfillwall,and considering the stiffness of the whole infill wall could lead to a crucial condition during the earthquakes. Thepresentworkaimstoevaluatethevariation inthelateralstrengthofthebuildingduetopresenceof centralopeningofaspectratioone,intheunreinforced masonryinfillwalls.Thevariousmodelswiththevarying percentageof centralopeningfrom10to35percenthave beenanalyzedbyseismicanalysismethodsprescribedby the Indian seismic code [1]. 2. MODELING AND ANALYSIS Inthepresentpaperlateralloadanalysisasperthe seismiccodeIS1893Part1-2002forthebarestructure and in filled structure are carried out and an effort is made tostudytheeffectofseismicloadsonthemandtheir capacityanddemandisevaluatedusingnonlinearstatic pushoveranalysis.Thegroundstoreyheightis4.8mand upper storeys height is 3.6m. Thebuilding is commercial building used for official purpose. The building is assumed tobelocatedinzoneIII,M-20gradeofconcreteandFe-415gradeofsteelareconsidered.DensityofRCis consideredas25Kn/m3,modulusofelasticityofbrick masonry is 2100 x 103 KN/m2. 2.1 Member Properties Table -1: Member properties Beam size0.30 x 0.45 m Column size (mid & core)0.30 x 0.60 m (peripheral)0.30 x 0.45m International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1448 2.2 Analytical Procedure For Modeling Inthepresentproject,3dmodelsandanalysesiscarried outbyutilizingtheETABSNonlinearsoftware.The softwareisabletoperformthegeometricnonlinear analysisofspaceframesunderstaticloading,takinginto accountbothgeometricnonlinearityandmaterial inelasticity,italsoconsiderstheP-effect.Thesoftware acceptsstaticloads(eitherforcesordisplacements)as well as dynamic (accelerations) actions and has the ability toperformeigenvalueanalysis,nonlinearstaticpushover and linear dynamic analyses. The analysis and design of the building is carried out using ETABScomputerprogram.Thefollowingtopicsdescribe some of the important areas in the modeling. 2.3 Models Considered Inthepresentpaperthree-dimensionalRCmultistorey buildingsofthreestoreysisconsidered.Theplanand elevationareshowninFig.1andFig2.The3Dviewand elevationsofdifferentbuildingmodelsconsideredare showninFigs.3.Thebuildingisdeliberatelykept symmetricinboththeorthogonaldirectionsinplanto avoidtorsionalresponseunderpurelateralforces.The analytical models considered are as below, 1stmodel:Buildingisconsideredasbareframestructure i.ethebuildingsatfirststoreyhasnowallsbutinthe upper storeys the unreinforced brick masonry infill wall is consideredhoweverthestiffnessisnottakeninto consideration but masses are included. 2nd model: The building at first storey has no walls but in theupperstorey'stheunreinforcedbrickmasonryinfill wallisconsideredhoweverthestiffnessisalsotakeninto consideration along with the masses. 3rd model : The building at first storey has no walls but in theupperstorey'stheunreinforcedbrickmasonryinfill wall with opening size of 10% of the total area at center is consideredandevenstiffnessandmassesaretakeninto consideration. 4th Model : The building at first storey has no walls but in theupperstorey'stheunreinforcedbrickmasonryinfill wall with opening size of 20% of the total area at center is consideredandevenstiffnessandmassesaretakeninto consideration. 5th Model : The building at first storey has no walls but in theupperstorey'stheunreinforcedbrickmasonryinfill wall with opening size of 30% of the total area at center is consideredandevenstiffnessandmassesaretakeninto consideration. 6th Model : The building at first storey has no walls but in theupperstorey'stheunreinforcedbrickmasonryinfill wall with opening size of 35% of the total area at center is consideredandevenstiffnessandmassesaretakeninto consideration. Fig -1: Plan of the building. Fig-2:Elevationofthreestoreyedinfillframebuilding models with openings (10% to 35%). International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1449 Fig -3: 3D view of three storeyed bare frame building 3. RESULTS AND DISCUSSION 3.1 Fundamental Natural Periods Thecodal(IS 1893 (Part1): 2002)andanalytical(ETABS) fundamentalnaturalperiodsofthevariousbuilding modelsaretabulatedinthetable2.Thevariationsofthe fundamentalnaturalperiodofallthesixmodelsfor 1.2(DL+LL+EL)loadcombinationsaretabulatedinbelow table. Table-2:Fundamentalnaturalperiodfor1.2(DL+LL+EL) seismic-designed buildings. Model No Analytical (sec) Code (sec) 3 Storey3 Storey 11.5050.330(78.07%) 21.2090.197(83.71%) 31.2450.197(84.18%) 41.3060.197(84.92%) 51.3710.197(85.63%) 61.4210.197(86.14%) Fromtheabovetableitisveryclearthat,stiffnessofthe buildingisdirectlyproportionaltoitsnaturalfrequency andhenceinverselyproportionaltothenaturalperiod. Thatis,ifthestiffnessofbuildingisincreasedthenatural periodgoesondecreasing.Thevariationofthenatural periodfromthemodel1tomodel6,illustratethatthe presenceoftheopeningintheinfillwallreducesthe stiffnessofthebuilding,therebyincreasingthenatural period,andtheamountofreductioninthestiffness depends on the percentage of opening. 3.2 Base Shear Thebaseshearfortheequivalentstaticmethod(VB) calculatedthroughetabsmodelingandmanually calculated base shear as per ID 1893 (Part 1):2002, for the various building models are listed in the table below. Table -3: Base shear for three storeyed building models Model No Longitudinal Direction Transverse Direction BV(kN) VB (kN) BV(kN) VB (kN) 1.2(DL+LL+EL) Seismic-designed Building Models 11639.072002.11639.072002.1 22553.252002.12553.252002.1 32333.421915.72333.421915.7 42216.511829.32216.511829.3 52079.461742.92079.461742.9 61957.221699.71957.221699.7 Thebaseshearisafunctionof mass,stiffness,height,and thenaturalperiodofthebuildingstructure.Fromthe previousresultsitisveryclearthatthefundamental natural periods obtained from the code, fall far short from that of the analytical natural periods. Fromtheaboveresultsitisobservedthat,the base shear in three storey building models as the stiffness and the mass of the infill wall reduces with the increase in percentageofopeningthebasesheargoesondecreasing atanaveragerateof6.4%formodel2tomodel6for equivalentstaticmethodalongboththelongitudinaland transverse directions. International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1450 3.3 Lateral Displacement Thelateraldisplacementsobtainedforequivalentstatic methodforthreestoreybuildingmodels,alongboththe longitudinal and transverse direction are listed in the table below. Table-4:Lateraldisplacement(mm)ofthreestoreyed modelsfor1.2(DL+LL+EL)seismic-designedbuildings (Equivalent static method). Storey No Model No 123456 Longitudinal Direction 320.611.612.413.915.216.7 214.811.512.413.513.914.2 114.111.111.512.112.913.5 Transverse Direction 325.417.518.219.920.522.5 221.717.517.919.619.920.5 121.117.417.71919.920.1 Fig-4:Lateraldisplacementofthreestoreyedmodelsfor 1.2(DL+LL+EL) seismic designed buildings. Thelateraldisplacementofabuildingisafunctionofthe stiffness,thelateraldisplacementofthestructurewill decreasewhenthelateralstiffnessincreases;hencethe displacementofthemodel2islessthanthemodel1.For threestoreyedbuildingsthepercentagereductionsinthe lateraldisplacementforequivalentstaticmethod,of model2whencomparedwithmodel1are43.6%and 31.1%for1.2(DL+LL+EL)seismic-designedbuilding modelsalongboththelongitudinalandtransverse directions respectively. Asthestiffnessofwallsisnotconsideredfor model1(bareframe)thevariationofthelateralstorey displacement curve is linear in nature. And for the model 2 the ground floor dont have the infill walls and the stiffness oftheupperstoreywallsisconsidered,asthestiffnessof onlyupperstoreywallsisconsidered,alltheupper storeysactasasinglestructureandmovesalmost together,andgroundfloorcolumnssufferthelarger displacement as shown in the above figure. As the stiffness decreases from model 2 to model 6 dueto theincreaseinthepercentageofcentralopening,the lateral displacement increases from model 2 to model 6. 3.4 Inter Storey Drift Interstoreydriftscalculatedforallthebuildingmodels alongboththelongitudinalandtransversedirectionsfor the Equivalent Static method are listed in the tables below. Table -5: Inter storey drift (mm) of three storeyed models for 1.2(DL+LL+EL) seismic designed buildings (Equivalent static method) Storey No Model No 123456 Longitudinal Direction 31.6240.0290.0720.1360.4440.923 22.0840.1070.1860.3690.9581.509 13.8912.3172.4222.5272.6542.764 Transverse Direction 31.5930.0060.0330.0830.3270.667 22.4760.0110.0570.1920.7921.389 15.2563.6333.7893.954.2254.327 International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1451 Fig-4:Storeydriftsofthreestoreyedmodelsfor 1.2(DL+LL+EQx) seismic designed buildings. Fig-5:Storeydriftsofthreestoreyedmodelsfor 1.2(DL+LL+EQy) seismic designed buildings. 3.5. Performance Evaluation Of Building Models Performance based seismic evaluation of all the six models is carried out by nonlinear static pushover analysis, for all theseismic-designedbuildingmodelsalongboth longitudinal and transverse directions. 3.5.1 Location Of Hinges And Performance Point Thebaseforceandthedisplacementattheperformance point(PP),andthelocationofthehingesalongboththe longitudinalandtransversedirectionsforallthebuilding models are tabulated in table below. Table-6:Performancepointandlocationofhingesfor threestoreyed1.2(DL+LL+EL)seismicdesignedbuilding modelsalonglongitudinaldirectionforEQX(Equivalent Static Method) Model No Performance Point Location of Hinges Base Force (kN) Displacement (mm) A-B B-IO IO-LS LS-CP CP-C C-D D-E >E TOTAL 118792.461536164160400576 218298.63377616 16 60200816 318542.22778012 12 100200816 418491.34476412 28 110100816 519050.64474428 20 210300816 619087.35474420 12 370300816 Table-7:Performancepointandlocationofhingesfor threestoreyed1.2(DL+LL+EL)seismicdesignedbuilding modelsalonglongitudinaldirectionforEQY(Equivalent Static Method) Model No Performance Point Location of Hinges Base Force (kN) Displacement (mm) A-B B-IO IO-LS LS-CP CP-C C-D D-E >E TOTAL 117535.78554048200400 576 217896.654783916 70100 816 318228.7567761216 110100 816 417112.56678816460200 816 517791.26979640140200 816 617354.675780128140200 816 Seismicevaluationofbuildingmodelsforthreestoreyed, iscarriedoutusingnonlinearstaticpushoveranalysis method,afteranalysisanddesignofthebuildingmodels accordingtoIS:456-2000usingthedesignfeatureof ETABS. Thebaseforceof thebuildingwhichisdependent onthelateralstrength,asthestiffnessofwallsis consideredinsoftstoreyedbuildings,thebaseforceis morethanthatofbareframe.Andforallbuildingmodels forthreestoreysthebaseforceatperformancepoint alonglongitudinaldirectionismorethanthatalong transverse direction. Duetoincreaseintheopeningpercentageinthe infill wall the stiffness goes on decreasing due to which the baseforceattheperformancepointalsodecreasesfrom model 2 to model 6.4. CONCLUSION Fromtheresultsdiscussedinthispaperwithrespectto thebuildingmodelsconsideredleadstothefollowing conclusions: Fundamentalnaturalperiodofthebuildingisa functionofitslateralstiffness,thereforefundamental natural period increases with increase in the percentage of opening. The stiffness of masonryinfillwall should notbe consideredifthepercentageofcentralopeningismore than 40%. Fundamental natural periods obtained from codal empirical formula (IS 1893: 2002 (Part 1)) are lesser than actual fundamental natural period (ETABS 9.1.1). Base shear of the building is directly proportional tothelateralstiffnessandthemassof thebuilding,asthe stiffness of the building decreases with the increase in the percentageofcentralopeningfrommodel2tomodel6, the base shear decreases at an average rate of 6.4%. Lateraldisplacementattheroofofbuilding models,increaseswiththeincreaseincentralopeningin themasonryinfillwalls,anditisfoundmoreforthe International Research Journal of Engineering and Technology (IRJET)e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015www.irjet.net p-ISSN: 2395-0072 2015, IRJET.NET- All Rights Reserved Page 1452 buildingmodelswiththepercentageofcentralopening more than the 30%.Duetothesoftgroundstorey,thestoreydriftis found more in the ground storey.Thebaseforceattheperformancepoint decreaseswiththeincreaseinthepercentageofcentral opening in the masonry infill wall. REFERENCES [1] IS: 1893(Part1)-2002, Criteria for earthquake resistant design of structure, General Provision and Building.[2]IS:456-2000CodeofPracticeforPlainandReinforced Concrete, Bureau of Indian Standards, New Delhi, India [3]Amlank.SenguptaandHimanshuGoyal(2008). Indicesforassessingseismicvulnerabilityofbuildings basedonlinearandnon-linearstaticanalysesJournalof Structural Engineering, Vol.35, No.1, April-May 2008 pp.9-15. [4]M.M.Maniyar,R.K. Khare,S GhoshandT. Chakrapani (2008).Seismiccollapseofnon-seismicRCframes JournalofStructuralEngineering,Vol.35,No.1,April-May 2008 pp.1-8. [5]B.PAnnapurnaandH.SharadaBaiEffectofSizeof OpeningswithintheInfillontheMembersof MultistoreyedInfillFrame,StructuralEngineering Convention,anInternationalmeet,Dec14-16,2006, Department of Civil Engineering, IISc Bangalore. [6]Kanitkar,R.andKanitkar,V.(2004),Seismic performanceofconventionalmulti-storeybuildingswith opengroundfloorsforvehicularparking,TheIndian Concrete Journal February 2004, pp 99-104 [7]GMondalandSKJainLateralStiffnessof UnreinforcedBrickInfilledRCFrameswithCentral Openings Proceedings of the 8th U.S. National Conference onEarthquakeEngineering,April18-22,2006,San Francisco, California, USA .BIOGRAPHIES TheauthorisfinalyearMtech CADstructuralcivilengineering departmentfromSDMCET DharwadaffiliatedtoVTU Belgaum. TheauthoriscurrentlyWorking asAssistantProfessorinCivil Engg.DepartmentofSDMCET DharwadaffiliatedtoVTU Belgaum.