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外文翻译--应用新型延性纤维增强聚合物对混凝土梁的加固 英文版.pdf

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外文翻译--应用新型延性纤维增强聚合物对混凝土梁的加固 英文版.pdf

692ACIStructuralJournal/SeptemberOctober2002ACIStructuralJournal,V.99,No.5,SeptemberOctober2002.MSNo.01349receivedOctober23,2001,andreviewedunderInstitutepublicationpolicies.Copyright©2002,AmericanConcreteInstitute.Allrightsreserved,includingthemakingofcopiesunlesspermissionisobtainedfromthecopyrightproprietors.PertinentdiscussionwillbepublishedintheJulyAugust2003ACIStructuralJournalifreceivedbyMarch1,2003.ACISTRUCTURALJOURNALTECHNICALPAPERAninnovative,uniaxialductilefiberreinforcedpolymerFRPfabrichasbeenresearched,developed,andmanufacturedintheStructuralTestingCenteratLawrenceTechnologicalUniversityforstrengtheningstructures.Thefabricisahybridoftwotypesofcarbonfibersandonetypeofglassfiber,andhasbeendesignedtoprovideapseudoductilebehaviorwithalowyieldequivalentstrainvalueintension.Theeffectivenessandductilityofthedevelopedfabrichasbeeninvestigatedbystrengtheningandtestingeightconcretebeamsunderflexuralload.Similarbeamsstrengthenedwithcurrentlyavailableuniaxialcarbonfibersheets,fabrics,andplateswerealsotestedtocomparetheirbehaviorwiththosestrengthenedwiththedevelopedfabric.Thefabrichasbeendesignedsothatithasthepotentialtoyieldsimultaneouslywiththesteelreinforcementofstrengthenedbeamsandhence,aductileplateausimilartothatforthenonstrengthenedbeamscanbeachieved.Thebeamsstrengthenedwiththedevelopedfabricexhibitedhigheryieldloadsandachievedhigherductilityindexesthanthosestrengthenedwiththecurrentlyavailablecarbonfiberstrengtheningsystems.Thedevelopedfabricshowsamoreeffectivecontributiontothestrengtheningmechanism.Keywordsconcreteductilityfiberreinforcementflexure.INTRODUCTIONTheuseofexternallybondedfiberreinforcedpolymerFRPsheetsandstripshasrecentlybeenestablishedasaneffectivetoolforrehabilitatingandstrengtheningreinforcedconcretestructures.SeveralexperimentalinvestigationshavebeenreportedonthebehaviorofconcretebeamsstrengthenedforflexureusingexternallybondedFRPplates,sheets,orfabrics.SaadatmaneshandEhsani1991examinedthebehaviorofconcretebeamsstrengthenedforflexureusingglassfiberreinforcedpolymerGFRPplates.Ritchieetal.1991testedreinforcedconcretebeamsstrengthenedforflexureusingGFRP,carbonfiberreinforcedpolymerCFRP,andG/CFRPplates.Graceetal.1999andTriantafillou1992studiedthebehaviorofreinforcedconcretebeamsstrengthenedforflexureusingCFRPsheets.Norris,Saadatmanesh,andEhsani1997investigatedthebehaviorofconcretebeamsstrengthenedusingCFRPunidirectionalsheetsandCFRPwovenfabrics.Inalloftheseinvestigations,thestrengthenedbeamsshowedhigherultimateloadscomparedtothenonstrengthenedones.Oneofthedrawbacksexperiencedbymostofthesestrengthenedbeamswasaconsiderablelossinbeamductility.Anexaminationoftheloaddeflectionbehaviorofthebeams,however,showedthatthemajorityofthegainedincreaseinloadwasexperiencedaftertheyieldofthesteelreinforcement.Inotherwords,asignificantincreaseinultimateloadwasexperiencedwithoutmuchincreaseinyieldload.Hence,asignificantincreaseinservicelevelloadscouldhardlybegained.Apartfromtheconditionoftheconcreteelementbeforestrengthening,thesteelreinforcementcontributessignificantlytotheflexuralresponseofthestrengthenedbeam.Unfortunately,availableFRPstrengtheningmaterialshaveabehaviorthatisdifferentfromsteel.AlthoughFRPmaterialshavehighstrengths,mostofthemstretchtorelativelyhighstrainvaluesbeforeprovidingtheirfullstrength.BecausesteelhasarelativelylowyieldstrainvaluewhencomparedwiththeultimatestrainsofmostoftheFRPmaterials,thecontributionofboththesteelandthestrengtheningFRPmaterialsdifferwiththedeformationofthestrengthenedelement.Asaresult,steelreinforcementmayyieldbeforethestrengthenedelementgainsanymeasurableloadincrease.SomedesignersplaceagreaterFRPcrosssection,whichgenerallyincreasesthecostofthestrengthening,toprovideameasurablecontribution,evenwhendeformationsarelimitedbeforetheyieldofsteel.Debondingofthestrengtheningmaterialfromthesurfaceoftheconcrete,however,ismorelikelytohappeninthesecasesduetohigherstressconcentrations.Debondingisoneofthenondesiredbrittlefailuresinvolvedwiththistechniqueofstrengthening.Althoughusingsomespeciallowstrainfiberssuchasultrahighmoduluscarbonfibersmayappeartobeasolution,itwouldresultinbrittlefailuresduetothefailureoffibers.TheobjectiveofthispaperistointroduceanewpseudoductileFRPfabricthathasalowstrainatyieldsothatithasthepotentialtoyieldsimultaneouslywiththesteelreinforcement,yetprovidethedesiredstrengtheninglevel.RESEARCHSIGNIFICANCEFRPshavebeenincreasinglyusedasmaterialsforrehabilitatingandstrengtheningreinforcedconcretestructures.CurrentlyavailableFRPmaterials,however,lacktheductilityandhavedissimilarbehaviorstosteelreinforcement.Asaresult,thestrengthenedbeamsmayexhibitareducedductility,lackthedesiredstrengtheninglevel,orboth.ThisstudypresentsaninnovativepseudoductileFRPstrengtheningfabric.ThefabricprovidesmeasurablyhigheryieldloadsforthestrengthenedbeamsandhelpstoavoidthelossofductilitythatiscommonwiththeuseofcurrentlyavailableFRP.DEVELOPMENTOFHYBRIDFABRICToovercomethedrawbacksmentionedpreviously,aductileFRPmaterialwithlowyieldstrainvalueisneeded.Titleno.99S71StrengtheningofConcreteBeamsUsingInnovativeDuctileFiberReinforcedPolymerFabricbyNabilF.Grace,GeorgeAbdelSayed,andWaelF.Ragheb693ACIStructuralJournal/SeptemberOctober2002LiteraturereviewonhybridizationTodevelopthismaterial,hybridizationfordifferentfiberswasconsidered.Hybridizationofmorethanonetypeoffibrousmaterialswastheinterestofmanymaterialsscienceresearchers.Mostoftheirworkwasconcernedwithcombiningtwotypesoffiberstoenhancethemechanicalpropertiesofeithertypeactingaloneandtoreducethecost.ThishasbeenreportedinseveralpublicationssuchasBunsellandHarris1974,Philips1976,MandersandBader1981,ChowandKelly1980,andFukudaandChow1981.HybridizationinterestedstructuralengineersasatooltoovercometheproblemofalackofductilityinFRPreinforcingbars.Nanni,Henneke,andOkamoto1994studiedbarsofbraidedaramidfibersaroundasteelcore.TamuzsandTepfers1995reportedexperimentalinvestigationsforhybridfiberbarsusingdifferentcombinationsofcarbonandaramidfibers.Somboonsong,Frank,andHarris1998developedahybridFRPreinforcingbarusingbraidedaramidfibersaroundacarbonfibercore.Harris,Somboonsong,andFrank1998usedthesebarsinreinforcingconcretebeamstoachievethegeneralloaddeflectionbehaviorofconcretebeamsreinforcedwithconventionalsteel.DesignconceptandmaterialsTogenerateductility,ahybridizationtechniqueofdifferenttypesoffibershasbeenimplemented.Threefibershavebeenselectedwithadifferentmagnitudeofelongationsatfailure.Figure1showsthestressstraincurvesintensionfortheselectedcompositefibers,andTable1showstheirmechanicalproperties.Thetechniqueisbasedoncombiningthesefiberstogetherandcontrollingthemixtureratiosothatwhentheyareloadedtogetherintension,thefiberswiththelowestelongationLEfailfirst,allowingastrainrelaxationanincreaseinstrainwithoutanincreaseinloadforthehybrid.TheremaininghighelongationHEfibersareproportionedtosustainthetotalloaduptofailure.ThestrainvalueatfailureoftheLEfiberspresentsthevalueoftheyieldequivalentstrainofthehybrid,whiletheHEfiberstrainatfailurepresentsthevalueofultimatestrain.TheloadcorrespondingtofailureofLEfiberspresentstheyieldequivalentloadvalue,andthemaximumloadcarriedbytheHEfibersistheultimateloadvalue.UltrahighmoduluscarbonfibersCarbonNo.1havebeenusedasLEfiberstohaveaslowastrainaspossible,butnotlessthantheyieldstrainofsteelapproximately0.2forGrade60steel.Ontheotherhand,EglassfiberswereusedasHEfiberstoprovideashighastrainaspossibletoproduceahighductilityindextheratiobetweendeformationatfailureanddeformationatyield.HighmoduluscarbonfibersCarbonNo.2wereselectedasmediumelongationMEfiberstominimizethepossibleloaddropduringthestrainrelaxationthatoccursafterfailureoftheLEfibers,andalsotoprovideagradualloadtransitionfromtheLEfiberstotheHEfibers.Basedonthisconcept,auniaxialfabricwasfabricatedandtestedtocompareitsbehaviorintensionwiththetheoreticalpredictedloadingbehavior.Thetheoreticalbehaviorisbasedontheruleofmixtures,inwhichtheaxialstiffnessofthehybridiscalculatedbyasummationoftherelativestiffnessofeachofitscomponents.Thefabricwasmanufacturedbycombiningdifferentfibersasadjacentyarnsandimpregnatingtheminsideamoldbyanepoxyresin.Figure2showsaphotoofoneofthefabricatedsamples.Wovenglassfibertabswereprovidedatbothendsofthetestcouponstoeliminatestressconcentrationsatendfixturesduringtesting.Thecouponshadathicknessof2mm0.08in.andawidthof25.4mmACImemberNabilF.GraceisaprofessorandChairoftheStructuralTestingCenter,DepartmentofCivilEngineering,LawrenceTechnologicalUniversity,Southfield,Mich.HeisamemberofACICommittee440,FiberReinforcedPolymerReinforcementandJointACIASCECommittee343,ConcreteBridgeDesign.Hisresearchinterestsincludetheuseoffiberreinforcedpolymerinreinforcedandprestressedconcretestructures.GeorgeAbdelSayedisProfessorEmeritusintheDepartmentofCivilandEnvironmentalEngineering,UniversityofWindsor,Windsor,Ontario,Canada.Hisresearchinterestsincludesoilstructureinteraction.WaelF.RaghebisaresearchassistantintheDepartmentofCivilEngineeringatLawrenceTechnologicalUniversity.HeisaPhDcandidateintheDepartmentofCivilandEnvironmentalEngineering,UniversityofWindsor,Windsor,Ontario,Canada.Fig.1Stressstrainbehaviorofcompositefibersandsteelreinforcingbars.Compositepropertiesarebasedon60fibervolumefraction.Table1MechanicalpropertiesofcompositefibersFibermaterialDescriptionModulusofelasticity,GPaMsiTensilestrength,MPaksiFailurestrain,CarbonNo.1Ultrahighmoduluscarbonfibers3795513241920.35CarbonNo.2Highmoduluscarbonfibers23133.524133500.9to1.0GlassEglassfibers48710341502.1Fig.2Testsamplefordevelopeduniaxialhybridfabric.Fig.3Resultsoftensiletestsfordevelopedhybridfabric.694ACIStructuralJournal/SeptemberOctober20021in.andweretestedintensionaccordingtoASTMD3039specifications.TheaverageloadstraincurveforfourtestedsamplesisshowninFig.3togetherwiththetheoreticalprediction.Itshouldbenotedthatthebehaviorislinearuptoastrainof0.35,whentheLEfibersstartedtofail.Atthispoint,thestrainincreasedatafasterratethantheload.Whenthestrainreached0.90,theMEfibersstartedtofail,resultinginanadditionalincreaseinstrainwithoutasignificantincreaseinload,uptothetotalfailureofthecouponbyfailureoftheHEfibers.Ayieldequivalentloadthefirstpointontheloadstraincurvewherethebehaviorbecomesnonlinearof0.46kN/mmwidth2.6kips/in.andanultimateloadof0.78kN/mm4.4kips/in.areobserved.BEAMTESTSBeamdetailsThirteenreinforcedconcretebeamswithcrosssectionaldimensionsof152x254mm6x10in.andlengthsof2744mm108in.werecast.TheflexurereinforcementofthebeamsconsistedoftwoNo.516mmtensionbarsnearthebottom,andtwoNo.39.5mmcompressionbarsnearthetop.Toavoidshearfailure,thebeamswereoverreinforcedforshearwithNo.39.5mmclosedstirrupsspacedat102mm4.0in..Fivebeamswereformedwithroundedcornersof25mm1in.radiustofacilitatetheinstallationofthestrengtheningmaterialontheirsidesandbottomfaceswithoutstressconcentrations.Figure4showsthebeamdimensions,reinforcementdetails,supportlocations,andlocationofloadingpoints.ThesteelusedwasGrade60withayieldstrengthof415MPa60,000psi,whiletheconcretecompressivestrengthatthetimeoftestingthebeamswas55.2MPa8000psi.StrengtheningmaterialsThedevelopedhybridfabricwasusedtostrengtheneightbeams.Twodifferentthicknessesoffabricwereused.ThefirstHsystem,t1.0mmhadathicknessof1.0mm0.04in.,andthesecondHsystem,t1.5mmhadathicknessof1.5mm0.06in..Fourotherbeamswerestrengthenedwiththreecurrentlyavailablecarbonfiberstrengtheningmaterials1auniaxialcarbonfibersheetwithanultimateloadof0.34kN/mm1.95kips/in.2twolayersofauniaxialcarbonfiberfabricwithanultimateloadof1.31kN/mm7.5kips/in.forthetwolayerscombinedand3apultrudedcarbonfiberplatewithanultimateloadof2.8kN/mm16kips/in..ThetestedloadstraindiagramsforFig.4Detailsoftestbeams.Fig.5Comparisonbetweencarbonfiberplate,fabric,sheet,anddevelopedhybridfabricHSystem.ACIStructuralJournal/SeptemberOctober2002695allthesematerialsareshowninFig.5.Table2showsthepropertiesofthestrengtheningmaterials,includingthedevelopedfabric.AdhesivesForthehybridfabric,anepoxyresinEpoxyAwasusedtoimpregnatethefibersandasanadhesivebetweenthefabricandtheconcretesurface.Thisepoxyhadanultimatestrainof4.4toensurethatitwouldnotfailbeforethefailureofthefibers.Forthebeamsstrengthenedwithcarbonfibersheets,plates,andfabric,anepoxyresinwithanultimatestrainof2.0wasusedEpoxyB.ThemechanicalpropertiesoftheadhesivesprovidedbytheirmanufacturesareshowninTable3.StrengtheningThebeambottomfacesandsidesweresandblastedtoroughenthesurface.Thebeamswerethencleanedwithacetonetoremovedirt.Twostrengtheningconfigurationswereused1strengtheningmaterialonthebottomfaceofthebeamonlyBeamGroupAand2strengtheningmaterialonthebottomfaceandextendedup152mm6in.onbothsidestocoverapproximatelyalltheflexuraltensionportionsofthebeamBeamGroupB.Thestrengtheningwasinstalledfor2.24m88in.,centeredalongthelengthofthebeam.Theepoxywasallowedtocureforatleast2weeksbeforethebeamsweretested.ForthebeamsstrengthenedwiththedevelopedhybridfabricHsystem,twobeamswerefabricatedandtestedforeachconfigurationtoverifytheresults.Table4summarizesthetestbeams.InstrumentationTheFRPstrainatmidspanwasmeasuredbythreestraingageslocatedatthebottomfaceofthebeam.ThesteeltensilestrainwasmeasuredbymonitoringthestrainonthesidesurfaceofthebeamatreinforcingbarlevelusingaDEMECdetachablemechanicalgagewithgagepointsforBeamGroupA,whilestraingageswereusedforBeamGroupB.Themidspandeflectionwasmeasuredusingastringpotentiometer.Thebeamswereloadedusingahydraulicactuator.Theloadwasmeasuredbymeansofaloadcell.Allthesensorswereconnectedtoadataacquisitionsystemtoscanandrecordthereadings.TESTRESULTSANDDISCUSSIONControlbeamThecontrolbeamhadayieldloadof82.3kN18.5kipsandanultimateloadof95.7kN21.5kips.Thebeamfailedbytheyieldingofsteel,followedbycompressionfailureofconcreteatthemidspan.TestresultsforthecontrolbeamareshowninthefiguresofthetestresultsofthestrengthenedbeamsFig.6through15.BeamGroupABeamGroupAcontainsthebeamsstrengthenedatthebottomfaceonly.Figure6to11showthetestresultsforthesebeams.TheresultsofBeamsH501andH751wereCommerciallyavailable.†Developedductilehybridsystem.Table2PropertiesofstrengtheningmaterialsTypeYieldequivalentload,kN/mmkips/in.Yieldequivalentstrain,Ultimateload,kN/mmkips/in.Ultimatestrain,Thickness,mmin.Carbonfibersheet0.341.951.20.130.005Carbonfiberplate2.816.01.41.30.05Carbonfiberfabric1.317.501.41.900.075Hsystem†t1mm0.231.300.350.392.241.741.00.04Hsystem†t1.5mm0.341.950.350.593.361.741.50.06Table3PropertiesofepoxyadhesivesEpoxytypeTensilestrength,MPaksiUltimatestrain,Compressivestrength,MPaksiA66.39.624.4109.215.84B68.910.02.086.212.50Fig.6BehaviorofBeamC1.Table4SummaryoftestbeamsBeamgroupBeamdesignationStrengtheningmaterialN/AControlN/AGroupAC1CarbonfibersheetC2CarbonfiberplateC3CarbonfiberfabricH501Hsystemt1mmH502H751Hsystemt1.5mmH752GroupBCSCarbonfibersheetHS501Hsystemt1mmHS502HS751Hsystemt1.5mmHS752

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