外文翻译钢板包裹的钢筋混凝土柱受冲力影响下的性能Word文档格式.docx

外文翻译钢板包裹的钢筋混凝土柱受冲力影响下的性能Word文档格式.docx

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原文

BehaviourofSteelPlatedRCColumnsSubjecttoLateralLoading

GriffithMC,WuYF,OehlersDJ.

Abstract:

ThemainfocusofthispaperistodescribethebehaviourofRCcolumnsthatare

retrofittedwithanalternativetechniqueto“jacketing”orwrapping.Thisnewtechniqueconsistsofattachingsteelplatestothetlexuralfacesofaconcretecolumnusingbolts.Itisenvisagedthatthistechniquewouldbesuitableprimarilyforcolumnshavingrectangularcross-sectionsandinsituationswherelateralloadinginducespredominatelyasingleplaneofbending（asopposedtobiaxialbending）.Effectivenessofthisnewtechniquehasbeendemonstratedbyexperimentaltestingandnumericalsimulations.Thispaperstudiesthemechanismofthenewretrofitscheme,howitworks,andthebehaviourofcolumnsretrofittedusingsuchascheme,aswellastheimportantparametersthataffecttheresponseoftheretrofittedcolumns.Thisstudyformsthebasisforthedesignoftheplateretrofittingsystem.

Keywords:

reinforcedconcrete,columns,numericalmodel,retrofitting,partialinteraction,slip.

1.INTRODUCTION

Theoreticalandexperimentalstudieshavedemonstratedthatexternaljacketingcanbehighlyeffectiveinpreventingexistingcolumnsfromprematureshear,lapspltceorflexuralfailureinthecaseofcircularcolumns.Therefore,thiskindofretrofittingworkhasalreadybeenwidelyusedinengineering（Chaietal.1991,1994;

Priestleyetal.1994a,b）.However,itisnotquiteasclear-cutforrectangularRCcolumnswherethesuccessoftheretrofitproceduredependson

thedegreetowhichjacketingincreasesconfinement.Forexample,Park（2001）states“Arectangularthinsteeljacketwouldnotbesoeffective,duetothesidesbowingoutwhendilationoftheconcreteoccursduringamajorearthquake,resultinginconfinementappliedmainlyinthecolumncorners”.Althoughrectangularjacketingcanstillbeeffectiveincertaincircumstances,therelativepoorperformanceofrectangularjacketsinconfiningtheconcretecorehasbeenexperimentallyverified（Chaietal.1990;

Mirmiranetal.1998,2000;

Pessikietal.2001）andTheriaultandNeale（2000）concludedthattheconfinementeffectivenessbyFRP（FibreReinforcedPolymer）wrappingisfarlessforrectangularcolumnsthanitisforcircularcolumns.

Effortstoimprovetheconfinementeffectivenessrectangularjacketshavebeenreportedintheliterature.Onetechniquewastoenhancetheout-of-planflexuralstiffnessofthejacketbyusingadditionalstiffenersinthecross-section.However,testresultsshowedthattheimprovementwasnotsatisfactory（Chaietal.1990）.Theuseofanchorboltstoenhancetheconfinementfromrectangularsteeljacketwasshown（Aboutahaetal.1996）toalsoprovidelimitedimprovement.Anothertechniqueusedforrectangularcolumnjacketingemploysanellipticalshapedjacket.ResearchworkshasshownthatthistechniqueishighlyeffectiveforretrofittingRCcolumnswithrectangularshapedcross-sections（Priestleyetal.1994b,1995;

TengandLam2002）.Nevertheless,changingsquareorrectangularshapedcolumnsectionstocircularorellipticalsectionsbycircularorellipticaljacketingisnotalwaysdesirableorpracticalinengineering,especiallywherespaceislimitedasinbuildingstructures.

Therehasbeenmuchresearchintotheuseofadvancedcompositematerialssuchasfiberglassandcarbonfiberjackets/wrappingtoreplacesteeljacketsinrecentyears（Katsumataetal.1988;

Saadatmaneshetal.1994,1996;

PriestleyandSeible1995;

Seibleetal.1997;

XiaoandMa1995,1997;

MirmiranandShahawy1997;

HannaandJones1997;

Xiaoetal.1999;

Liuetal.2000;

Pantelidesetal.2000;

Karbhari2001;

TheriaultandNealc2000;

Yaoetal.2001;

LauandZhou2001;

Pessikietal.2001;

ParvinandWang2001;

LamandTeng2003a,b;

TengandLam2004）.Nevertheless,FRPjacketsliketheirsteelcounterparts,relyontheirabilitytoincreasetheconfinementoftheconcretecolumnsothatitsmaterialbehaviourbeyondthepeakcompressivestresspointisimproved.

Incontrastto“jacketing”retrofitschemes,theformofcompositeplatingdevelopedbytheauthorsisanewconceptforretrofittingrectangularRCcolumns.Itworks,essentially,bydelayingtheonsetofconcretecrushingthroughtheadditionofexternalsteelplatingthatactsonlyincompressionontheflexuralfacesoftheconcretecolumn.Bydelayingconcretecrushing,additionalcurvaturecanbesustainedbythecolumnbeforesubstantiallossofstrengthoccurs,resultinginsubstantiallyincreaseddisplacement/driftcapacity.Detailsofthenewretrofitschemearedescribedinthenextsection.（Note:

platebucklingofside-platedconcretebeamscanbepreventedthroughjudiciouschoiceofplatethicknessandboltspacing（Smithetal.1999）.Itisnotafocusofthispaperandwillnotbediscussedfurther.）

2.RETROFITSCHEMEBYPARTIALINTERACTIONPLATING

AschematicofthenewschemeisgiveninFigurelwherealengthofcolumnbetweenitsendandmidheightisshown.Steelplatesintheshapeofan“L”（asinFigurel（a）areboltedtoboththetensionandcompressionfacesofthecolumnandalsotothefoundationorbeam/slab（Figurel（a）andl（d））.Thenovelaspectofthisretrofitsolutionisthattheplateonthetensionfacecanbemadetoattractverylittletensionforce,intheplastichingezoneatthebaseofthecolumn,bypositioningtheboltsawayfromthejoint（Figurel（b）,l（c））.Ontheotherhand,theplateonthecompressionfacewillattractsignificantcompressiveforceduetothehighcompressionstiffnessoftheplates’endbearingcondition（Figurel（b））.Thus,thecrushingofconcreteisdelayedsubstantiallynotbyincreasedconcretecompressivestrengthduetoincreasedconfinementbutratherbyvirtueoftransferringthecompressionloadfromtheconcretetothesteelplate.Thishasthepotentialtosignificantlyincreaseeitherthestrengthortheductilityorbothofaconcretecolumn.

Themotivationforthisalternativeretrofitconceptisthatsubstantiallyimprovedconfinementthroughjacketingisnotalwaysachievableforrectangularcross-sections.Furthermanyconcreteframestructuresinlowtomoderateearthquakehazardregionshavebeendesignedpredominatelyforgravityandwindloadingbutmayhaveinsufficientlevelsofdisplacementductilitytowithstandsignificantearthquakeshaking.Inmanyinstances,thecolumnshavesufficientshearstrengthforthecolumnstoreachtheirultimatemomentcapacity.Inthepresentwork,ithasbeenassumedthatcolumnflexureoccursprimarilyina

singleplane.Forexample,bridgepierswhoseflexureinthelongitudinaldirectionisrestrictedduetotheaxialstiffnessofthebridgedeckanddisplacementconstraintsofthebridgeabutments.Inaddition,itisnotunusualtohavecolumnsinabuildingstructureparticipatinginmomentframeactionunderlateralloadingonlyinasingledirection.Forallofthesesituations,itmaybefeasibletoconsiderretrofitonlyforuni-directionalloadingratherthanbi-directionalloading.

Theeffectivenessofthenewretrofitschemehasbeendemonstratedexperimentally（Wuetal.2003）.Abriefdescriptionofthetestingisprovidedhere.ThetestconfigurationisillustratedinFigure2（a）withtheaxialloadN=360kNbeingappliedin“forcecontrol”modeandthelateralloadFbeingappliedin“displacementcontrol”mode.Inordertogettwotestsfromeachspecimen,oneendwastemporarilystrengthenedbysandwichingthecolumnbetweenlargesteelchannelsections（Figure2（b））sothatthedeformationsduetotheloadingoccurredonlyintheoppositeend.Thereinforcementdetailsforthecolumnsconsistedoffour16mmdeformedbarsand10mmstirrupsat100mmspacingasshowninFigure2（c）.Theretrofitschemedetailsforthetestcolumns（giveninTable1）consistedofboltingeither6mmor12mmthicksteelplateontothetensionandcompressionfacesofthecolumns.TheboltswereadhesivelyattachedtothecolumnusingHiltiHIT-HY150adhesive.Theinteractionorshearbetweentheboltsandthesteelplatewastransmittedbybearing.Theholesinthesteelplatewere0.2mmgreaterthanthediameterofthebolts.Thesteelplatejustsatonthecolumnbaseandnoothermeasurewasusedtopreventlocalconcretecrushingatbaseandbucklingofsteelplate.FormoredetailsofthetestinganddesignoftheplateandboltingpatternrefertoWu（2002）andWuetal（2003）.

PlotsofthelateralloadFversussideswaydeflection∆arepresentedinFigure3and

theresultsaresummarizedinTable2.Itshouldbenotedthatamoreuseful,non-dimensional,variableforexpressingthesideswayresponseisintermsof“drift”,definedhereas∆

dividedbythecolumnheightof1.218m.ThedriftresponseisalsoshowninFigure3onthetophorizontalaxis.Tocomparetheresponseofthethreecolumns,itisconvenientthentousedisplacementductility,definedbyEqn1,

µ

∆=∆u∆y

（1）

where∆y

istheyielddisplacement（thepointwherethetensilereinforcementfirstyields

andthemaximumstrengthisreached）,and

∆uisthelateraldisplacementatthepointwhere

thelateralresistanceforceequals80%ofthemaximumlateralforce.ThedisplacementductilityfactorsforthethreecurvesinFigure3arelistedinTable2whereitcanbeseenthatboththeplatedcolumnshadgreaterdisplacementductilitythantheunplatedcolumn.Similarbehaviourwasobservedinthecyclicloadingtests（Figure4）wherethe6mmplatedcolumn（4ACP6）wassignificant