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土木工程专业毕业设计外文文献及翻译
英文原文:
RehabilitationofrectangularsimplysupportedRCbeamswithsheardeficienciesusingCFRPcomposites
AhmedKhalifaa,*,AntonioNannib
aDepartmentofStructuralEngineering,UniversityofAlexandria,Alexandria21544,Egypt
bDepartmentofCivilEngineering,UniversityofMissouriatRolla,Rolla,MO65409,USA
Received28April1999;receivedinrevisedform30October2001;accepted10January2002
Abstract
Thepresentstudyexaminestheshearperformanceandmodesoffailureofrectangularsimplysupportedreinforcedconcrete(RC)beamsdesignedwithsheardeficiencies.Thesememberswerestrengthenedwithexternallybondedcarbonfiberreinforcedpolymer(CFRP)sheetsandevaluatedinthelaboratory.Theexperimentalprogramconsistedoftwelvefull-scaleRCbeamstestedtofailinshear.Thevariablesinvestigatedwithinthisprogramincludedsteelstirrups,andtheshearspan-to-effectivedepthratio,aswellasamountanddistributionofCFRP.TheexperimentalresultsindicatedthatthecontributionofexternallybondedCFRPtotheshearcapacitywassignificant.Theshearcapacitywasalsoshowntobedependentuponthevariablesinvestigated.Testresultswereusedtovalidateasheardesignapproach,whichshowedconservativeandacceptablepredictions.
2002ElsevierScienceLtd.Allrightsreserved.
Keywords:
Rehabilitation;Shear;Carbonfiberreinforcedpolymer
1.Introduction
Fiberreinforcedpolymer(FRP)compositesystems,composedoffibersembeddedinapolymericmatrix,canbeusedforshearstrengtheningofreinforcedcon-crete(RC)members[1–7].ManyexistingRCbeamsaredeficientandinneedofstrengthening.TheshearfailureofanRCbeamisclearlydifferentfromitsflexuralfailure.Inshear,thebeamfailssuddenlywithoutsufficientwarninganddiagonalshearcracksareconsid-erablywiderthantheflexuralcracks[8].
Theobjectivesofthisprogramwereto:
1.InvestigateperformanceandmodeoffailureofsimplysupportedrectangularRCbeamswithsheardeficien-ciesafterstrengtheningwithexternallybondedCFRPsheets.
2.Addressthefactorsthatinfluenceshearcapacityofstrengthenedbeamssuchas:
steelstirrups,shearspan-to-effectivedepthratio(a/dratio),andamountanddistributionofCFRP.
3.Increasetheexperimentaldatabaseonshearstrength-eningwithexternallybondedFRPreinforcement.
4.Validatethedesignapproachpreviouslyproposedbytheauthors[9].
Fortheseobjectives,12full-scale,RCbeamsdesignedtofailinshearwerestrengthenedwithdifferentCFRPschemes.Thesemembersweretestedassimplebeamsusingafour-pointloadingconfigurationwithtwodifferenta/dratios.
2.Experimentalprogram
2.1.Testspecimensandmaterials
Twelvefull-scalebeamspecimenswithatotalspanof3050mm.andarectangularcross-sectionof150-mm-wideand305-mm-deepweretested.ThespecimensweregroupedintotwomainseriesdesignatedSWandSOdependingonthepresenceofsteelstirrupsintheshearspanofinterest.
SeriesSWconsistedoffourspecimens.ThedetailsanddimensionsofthespecimensdesignatedseriesSWareillustratedinFig.1a.Inthisseries,four32-mmsteelbarswereusedaslongitudinalreinforcementwithtwoattopandtwoatbottomfaceofthecross-sectiontoinduceashearfailure.Thespecimenswerereinforcedwith10-mmsteelstirrupsthroughouttheirentirespan.Thestirrupsspacingintheshearspanofinterest,righthalf,wasselectedtoallowfailureinthatspan.
SeriesSOconsistedofeightbeamspecimens,whichhadthesamecross-sectiondimensionandlongitudinalsteelreinforcementasforseriesSW.NostirrupswereprovidedinthetesthalfspanasillustratedinFig.1b.
Eachmainseries(i.e.seriesSWandSO)wassubdividedintotwosubgroupsaccordingtoshearspan-to-effectivedepthratio.Thiswasselectedtobea/d=3and4,resultinginthefollowingfoursubgroups:
SW3;SW4;SO3;andSO4.
ThemechanicalpropertiesofthematerialsusedformanufacturingthetestspecimensarelistedinTable1.FabricationofthespecimensincludingsurfacepreparationandCFRPinstallationisdescribedelsewhere[10].
Table1
2.2.Strengtheningschemes
Onespecimenfromeachseries(SW3-1,SW4-1,SO3-1andSO4-1)wasleftwithoutstrengtheningasacontrolspecimen,whereaseightbeamspecimenswerestrengthenedwithexternallybondedCFRPsheetsfollowingthreedifferentschemesasillustratedinFig.2.
InseriesSW3,specimenSW3-2wasstrengthenedwithtwoCFRPplieshavingperpendicularfiberdirections(90°/0°).ThefirstplywasattachedintheformofcontinuousU-wrapwiththefiberdirectionorientedperpendiculartothelongitudinalaxisofthespecimen(90°).Thesecondplywasbondedonthetwosidesofthespecimenwiththefiberdirectionparalleltothebeamaxis(0°).Thisply[i.e.0°ply]wasselectedtoinvestigatetheimpactofadditionalhorizontalrestraintonshearstrength.
InseriesSW4,specimenSW4-2wasstrengthenedwithtwoCFRPplieshavingperpendicularfiberdirection(90°/0°)asforspecimenSW3-2.
FourbeamspecimenswerestrengthenedinseriesSO3.SpecimenSO3-2wasstrengthenedwithone-plyCFRPstripsintheformofU-wrapwith90°-fiberorientation.Thestripwidthwas50mmwithcenter-to-centerspacingof125mm.SpecimenSO3-3wasstrengthenedinamannersimilartothatofspecimenSO3-2,butwithstripwidthequalto75mm.SpecimenSO3-4wasstrengthenedwithone-plycontinuousU-wrap(90°).SpecimenSO3-5wasstrengthenedwithtwo
CFRPplies(90°/0°)similartospecimensSW3-2andSW4-2.
InseriesSO4,twobeamspecimenswerestrengthened.SpecimenSO4-2wasstrengthenedwithone-plyCFRPstripsintheformofU-wrapsimilartospecimenSO3-2.SpecimenSO4-3wasstrengthenedwithone-plycontinuousU-wrap(90°)similartoSO3-4.
Fig.1.Configurationandreinforcementdetailsforbeamspecimens.
Fig.2.SchematicrepresentationofCFRPstrengtheningschemes.
2.3.Testset-upandinstrumentation
Allspecimensweretestedassimplespanbeamssubjectedtoafour-pointloadasillustratedinFig.3.Auniversaltestingmachinewith1800KNcapacitywasusedinordertoapplyaconcentratedloadonasteeldistributionbeamusedtogeneratethetwoconcentratedloads.Theloadwasappliedprogressivelyincycles,usuallyonecyclebeforecrackingfollowedbythreecycleswiththelastoneuptoultimate.Theappliedloadvs.deflectioncurvesshowninthispaperaretheenvelopesoftheseloadcycles.
Fourlinearvariabledifferentialtransformers(LVDTs)wereusedforeachtesttomonitorverticaldisplacementsatvariouslocationsasshowninFig.3.TwoLVDTswerelocatedatmid-spanoneachsideofthespecimen.Theothertwowerelocatedatthespecimensupportstorecordsupportsettlement.
Fig.3.Schematicrepresentationoftestset-upforspecimen(a)SW3-1,and(b)SW3-2.
ForeachspecimenofseriesSW,sixstraingaugeswereattachedtothreestirrupstomonitorthestirrupstrainduringloadingasillustratedinFig.1a.ThreestraingaugeswereattacheddirectlytotheFRPsheetonthesidesofeachstrengthenedbeamtomonitorstrainvariationintheFRP.Thestraingaugeswereorientedintheverticaldirectionandlocatedatthesectionmid-heightwithdistancesof175,300and425mm,respectively,fromthesupportforseriesSW3andSO3.ForbeamspecimensofseriesSW4andSO4,thestraingaugeswerelocatedatdistanceof375,500and625mm,respectively,fromthesupport.
3.Resultsanddiscussion
Inthefollowingdiscussion,referenceisalwaysmadetoweakshearspanorspanofinterest.
3.1.SeriesSW3
ShearcracksinthecontrolspecimenSW3-1wereobservedclosetothemiddleoftheshearspanwhentheloadreachedapproximately90kN.Astheloadincreased,additionalshearcracksformedthroughout,wideningandpropagatinguptofinalfailureataloadof253kN(seeFig.4a).
InspecimenSW3-2strengthenedwithCFRP(90°/0°),nocrackswerevisibleonthesidesorbottomofthetestspecimenduetotheFRPwrapping.However,alongitudinalsplittingcrackinitiatedonthetopsurfaceofthebeamatahighloadofapproximately320kN.
Fig.4.FailuremodesofseriesSW3specimens.
Thecrackinitiatedatthelocationofappliedloadandextendedtowardsthesupport.Thespecimenfailedbyconcretesplitting(seeFig.4b)attotalloadof354kN.Thiswasanincreaseof40%inultimatecapacitycomparedtothecontrolspecimenSW3-1.Thesplittingfailurewasduetotherelativelyhighlongitudinalcompressivestressdevelopedattopofthespecimen,whichcreatedatransversetension,ledtothesplittingfailure.Inaddition,therelativelylargeamountoflongitudinalsteelreinforcementcombinedwithover-strengtheningforshearbyCFRPwrapprobablycausedthismodeoffailure.Theloadvs.mid-spandeflectioncurvesforspecimensSW3-1andSW3-2areillustratedinFig.5,toshowtheadditionalcapacitygainedbyCFRP.
Fig.5.Appliedloadvs.mid-spandeflectionforseriesSW3specimens.
ThemaximumCFRPverticalstrainmeasuredatfailureinspecimenSW3-2wasapproximately0.0023mm/mm,whichcorrespondedto14%ofthereportedCFRPultimatestrain.Thisvalueisnotanabsolutebecauseitgreatlydependsonthelocationofthestraingaugeswithrespecttoacrack.However,therecordedstrainindicatesthatifthesplittingdidnotoccur,theshearcapacitycouldhavereachedhigherload.
ComparisonbetweenmeasuredlocalstirrupstrainsinspecimensSW3-1andSW3-2areshowninFig.6.Thestirrups1,2and3werelocatedatdistanceof175,300and425mmfromthesupport,respectively.Theresultsshowedthatthestirrups2and3didnotyieldatultimateforbothspecimens.Thestrains(andtheforces)inthestirrupsofspecimenSW3-2were,ingeneral,s