汶川地震建筑损坏的分析 2.docx

汶川地震建筑损坏的分析 2.docx

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汶川地震建筑损坏的分析2

一、外文原文

Studyontheeffectoftheinfillwallsontheseismicperformanceofareinforcedconcreteframe

ZhangCuiqiang,ZhouYing,ZhouDeyuan,LuXilin

Abstract:

MotivatedbytheseismicdamageobservedtoreinforcedconcreteframestructuresduringtheWenchuanearthquake,theeffectofinfillwallsontheseismicperformanceofaRCframeisstudiedinthispaper.Infillwallsoffersomeamountofstiffnessandstrength.Therefore,theeffectofinfillwallsshouldbeconsideredduringthedesignofRCframes.Inthisstudy,ananalysisoftherecordedgroundmotionintheWenchuanearthquakeisperformed.Then,anumericalmodelisdevelopedtosimulatetheinfillwalls.Finally,nonlineardynamicanalysisiscarriedoutonaRCframewithandwithoutinfillwalls,respectively,byusingCANNYsoftware.Throughacomparativeanalysis,thefollowingconclusionscanbedrawn.Thefailuremodeoftheframewithinfillwallsisinaccordancewiththeseismicdamagefailurepattern,whichisstrongbeamandweakcolumnmode.ThenumericalmodelpresentedinthispapercaneffectivelysimulatetheeffectofinfillwallsontheRCframe.

Keywords:

infillwalls;RCframestructure;strongcolumnandweakbeam;strongbeamandweakcolumn;nonlineartimehistoryanalysis

1.Introduction

Inthefieldofengineering,itisgenerallyconsideredthatinfillwallsinaconcreteframeserveasanonstructuralelement.Inactualpractice,theinfluenceofinfillwallsofframestructuresisconsideredbyareductionfactortotheperiodofthereinforcedconcrete（RC）framewithoutinfillwalls.Thedisadvantageofthismethod,however,isthatitdisregardstheconstraintoftheinfillwallsontheRCframe.IntheWenchuanearthquake,manyframessufferedplastichingedamageatcolumnsinsteadofbeams,whichisdifferentfromthefailuremodeexpectedintheseismiccode.Theconstrainteffectoftheinfillwallschangesthefailuremodeoftheframe.

Someresearchers（QianandZhao,2008;Lietal.,2009;Yangetal.,2009;Guoetal.,2008）pointedoutthatinfillwallsinRCframeschangetheframefailuremodebychangingthestiffnessoftheRCframe.Others（ChakerandCherifati,1999;Shietal.,1996）whoconductedexperimentalstudiesconcludedthatthelocationoftheinfillwallsplaysdifferentrolesinthemechanicalpropertiesoftheframeandtheinfillwallscansometimesincreasetheframestiffnessasmuchasseventimesoverthebareframe.

Therefore,theeffectoftheinfillwallsmustbetakenintoaccountinthedesignoftheRCframeiftherequiredfailuremodeintheChineseseismiccodeistoberealized.Generally,therearethreemechanicalmodelsofinfillwallsintheRCframeasfollows:

（1）theeffectivestiffnessmodel（CodeforSeismicDesignBuildings,2001）.

（2）frame-infill-wallparallelmodel（Caoetal.,1997）,inwhichtheinfillwallsareconsideredastheshearwalltoworktogetherwiththeframe,theframeandinfillwallshavethesamedisplacement.Thestiffnessoftheinfillwallsadopts0.2-0.3timestheinitialstiffnessaftercracking;and（3）diagonalstrutmodel（MonicaPuglisietal.,2009）,inwhichtheinfillwallsareconsideredasthediagonalstrutandpinconnectionusedattheends.

Thefirstmodelcanconsiderthestiffnessoftheinfillwalls,butthelocationoftheinfillwallsintheRCframescannotbeconsidered.ThesecondmechanicalmodeldoesnottaketheconstraintbetweentheRCframeandinfillwallsintoaccount.Thethirdmechanicalmodelcantakethestiffnessoftheinfillwallsintoconsideration,butitdoesnotconsidertheco-workbehaviorofthebeamandthefilledwall.

Inthispaper,thediagonalstrutmodelisusedtosimulatethestiffnessoftheinfillwalls;meanwhileamodifiedsectionofbeamisusedtosimulatethecoworkbehavioroftheinfillwalls.Theresultsshowgoodagreementwiththeactualdamage.

2．Damageobservation

DuringtheWenchuanearthquake,manybuildingssufferedseveredamage.ManyRCframestructures,designedaccordingtothecode,developedacolumnhingemechanismwhichisdifferentfromthedesiredmechanismspecifiedintheChinacodeofseismicdesignofbuildings（CCSDB,GB50011-2001）.IntheCCSDB,abeamhingemechanismispreferredtodissipatetheearthquakeenergyandpreventcollapsewhensubjectedtoarareearthquake,witha2%to3%probabilityofexceedancein50years.However,theseismicbehaviorofRCframesintheWenchuanearthquakewasbeyondtheexpectationsofresearchers.TypicaldamagesuchasobservedinateachingschoolbuildinglocatedinDujiangyanispresented.

Differentextentsofdamageareseenonthetopendofthecolumnsinthefirstfloor.Muchcrackingwasobservedinthefirstfloorinfillwallsandtheveneerfelltotheground.Thereisnoobviousdamageonthesecondfloorexceptforsomecrackingintheinfillwallsandfallingofveneerinthestaircaseroom.

3Targetbuilding

ThetargetbuildinginthispaperislocatedintheDujiangyanCity,SichuanProvince.ThestructuralplanisshowninFig.3.ThespecificcrosssectioninformationispresentedinTable1.Becauseoftherequirementofthearchitecturalfunction,therearenoinfillwallsinthefirstfloorexceptforthreeareas.Thethicknessoftheinfillwallsis240mm.

4Analyticalmodel

4.1Assumption

Thecolumnendsinthispaperusefiberelementstosimulatethecouplingbehaviorbetweenthebiaxialbendingandaxialdeformation.Inthemiddleofthecolumn,abi-directionalshearspringelementisusedtosimulatethebi-directionalshearbehavior.Beamendsemployatri-linearspringelementtosimulatethebendingbehavior.Inthemiddleofthebeam,abi-linearspringelementisusedtosimulatetheshearbehavior.

Theconcreteconstitutivemodel（Hoshikumaetal.,1997）,andthesteelbarconstitutivemodel（Li,2004）.Theinfillwallsaresimulatedbythecompressiononlyelement.Thewidthofthesectionis0.25timesthelengthofthediagonalline（PaulayandPriestley,1991;Hu,2010）.Thenormalizedconstitutiverelationshipofthemasonryinfillwall（Zhu，1990）Theconstitutiverelationshipofthediagonalstrutisatri-linearspringmodel（KwonandKim,2009）.

Thetri-lineardisplacement-forcerelationshipconsistsofcrackingforce（F）,maximumcompressionforce,yielddisplacementandmaximumdisplacementatpeakforce（U）.Themasonrymaximumcompressionstraincorrespondingtothepeakcompressionstressisdefinedas0.005,andtheultimatestrainisdefinedas0.02.Thecrackingshearforceisdefinedas0.6timesthemaximumcompressionforce.

Inordertoconsidertheeffectoftheinfillwallsonthebeam,thebeamsectionismodifiedbyaddingone-thirdoftheinter-storyheightinfillwallsontotheoriginalRCcrosssectiontoformanenlargedcrosssection.Thewidthoftheflangeofthecrosssectionis12timesthethicknessoftheslab.Itisnecessarytousethemasonrywallpeakstressandultimatestrainintheconcreteconstitutiverelationshiptosimulatethepropertyoftheinfillwalls（Zhu,1990）.

4.2Recordedgroundmotions

Thepeakgroundacceleration（PGA）was652.9GalintheN-Sdirection,957.7galintheE-Wdirection,and

948.1GalintheU-Ddirection.Theearthquakelastedlongerthan120s,about180s.

AccordingtotheFourieramplitudespectrumsanalysis,themainfrequencyrangeinthehorizontaldirectionsis5-15Hz,andthemainfrequencyrangeintheverticaldirectionis5-60Hz.

4.3Analyticalmodelofthetargetbuilding

Inordertocomparetheeffectoftheinfillwalls,threemodelsareanalyzedinthispaper.OnemodelisthebareRCframe（withoutinfillwalls）,andtheothertwoareRCframeswithinfillwalls.ThedifferencebetweenthelattertwoRCframesisthatoneconsiderstheco-workoftheinfillwallsandbeamandtheotherdoesnot.

Iftheelementdevelopsanyoneoffollowingconditions,theelementwillbeconsideredtobeyielding（Li,2004）.

Definitionofyield:

（1）axialcompressionforceratio>0.6（over60%ofcentralcompressioncapacity）;

（2）steelbarsyield-ratio>0.5（halformoreofrebartension/compressionyielded）;

（3）rebarmaximumstrainintension>20.0e（steelbaryieldingstrain）;

（4）steel/rebarmaximumstrainincompression>5.0ey（steelbaryieldingstrain）;

（5）concretecompressionstrain>e0（concretestraincorrespondingtotheconcretepeakstress）.

5Analyticalresults

5.1Comparisonofdynamicproperties

Threeanalyticalmodelsarepresentedinthispaperothestudytheeffectoftheinfillwalls.Theyareasfollows:

（1）thefirstmodelisabareRCframethatdoesnotconsidertheinfillwalls;

（2）thesecondmodelisaRCframethatconsiderstheinfillwallsbythediagonalstrutanddoesnotconsidertheco-workofthebeamandinfillwalls;and（3）thethirdmodelisaRCframethatconsiderstheinfillwallsbythediagonalstrutandconsiderstheinteractionofthebeamandinfillwalls.

Fromthecomparison,theorderofthemodeshapeischangedbytheinfillwalls.ThefirstmodeshapechangesfromXdirectiontranslationtoYdirectiontranslation.Theinfillwallschangethemodeshapestiffnessofthestructure.ThemodestiffnessintheXdirectionisenhancedto2.92timestheoriginalmodeshapestiffness,and1.63timesintheYdirection.Thetorsionmodeshapeis1.79timestheoriginalone.

5.2Hysteresisloop

Fromthecomparisonofthehysteresisloop,theinfillwallsnotonlychangethestiffnessoftheRCframe,whichincreasestheshearforceoffloor,butalsochangethestrengthdistributionoftheRCframe,causingthefirstfloortobetheweakfloor.

6Conclusions

Thispaperpresentsananalysisoftheadvantagesanddisadvantagesofthreemechanicalmodelsusedtosimulateinfillwalls