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_第1页
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_第2页
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_第3页
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_第4页
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_第5页
已阅读5页,还剩4页未读 继续免费阅读

下载本文档

版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领

文档简介

692ACIStructuralJournal/September-October2002ACIStructuralJournal,V.99,No.5,September-October2002.MSNo.01-349receivedOctober23,2001,andreviewedunderInstitutepublicationpolicies.Copyright2002,AmericanConcreteInstitute.Allrightsreserved,includ-ingthemakingofcopiesunlesspermissionisobtainedfromthecopyrightproprietors.PertinentdiscussionwillbepublishedintheJuly-August2003ACIStructuralJournalifreceivedbyMarch1,2003.ACISTRUCTURALJOURNALTECHNICALPAPERAninnovative,uniaxialductilefiber-reinforcedpolymer(FRP)fabrichasbeenresearched,developed,andmanufactured(intheStructuralTestingCenteratLawrenceTechnologicalUniversity)forstrengtheningstructures.Thefabricisahybridoftwotypesofcarbonfibersandonetypeofglassfiber,andhasbeendesignedtoprovideapseudo-ductilebehaviorwithalowyield-equivalentstrainvalueintension.Theeffectivenessandductilityofthedevelopedfabrichasbeeninvestigatedbystrengtheningandtestingeightconcretebeamsunderflexuralload.Similarbeamsstrengthenedwithcurrentlyavailableuniaxialcarbonfibersheets,fabrics,andplateswerealsotestedtocomparetheirbehaviorwiththosestrengthenedwiththedevelopedfabric.Thefabrichasbeendesignedsothatithasthepotentialtoyieldsimultaneouslywiththesteelreinforcementofstrengthenedbeamsandhence,aductileplateausimilartothatforthenonstrengthenedbeamscanbeachieved.Thebeamsstrengthenedwiththedevelopedfabricexhibitedhigheryieldloadsandachievedhigherductilityindexesthanthosestrengthenedwiththecurrentlyavailablecarbonfiberstrengtheningsystems.Thedevelopedfabricshowsamoreeffectivecontributiontothestrengtheningmechanism.Keywords:concrete;ductility;fiberreinforcement;flexure.INTRODUCTIONTheuseofexternallybondedfiber-reinforcedpolymer(FRP)sheetsandstripshasrecentlybeenestablishedasaneffectivetoolforrehabilitatingandstrengtheningreinforcedconcretestructures.SeveralexperimentalinvestigationshavebeenreportedonthebehaviorofconcretebeamsstrengthenedforflexureusingexternallybondedFRPplates,sheets,orfabrics.SaadatmaneshandEhsani(1991)examinedthebehaviorofconcretebeamsstrengthenedforflexureusingglassfiber-reinforcedpolymer(GFRP)plates.Ritchieetal.(1991)testedreinforcedconcretebeamsstrengthenedforflexureusingGFRP,carbonfiber-reinforcedpolymer(CFRP),andG/CFRPplates.Graceetal.(1999)andTrian-tafillou(1992)studiedthebehaviorofreinforcedconcretebeamsstrengthenedforflexureusingCFRPsheets.Norris,Saa-datmanesh,andEhsani(1997)investigatedthebehaviorofconcretebeamsstrengthenedusingCFRPunidirectionalsheetsandCFRPwovenfabrics.Inalloftheseinvestigations,thestrengthenedbeamsshowedhigherultimateloadscom-paredtothenonstrengthenedones.Oneofthedrawbacksexperiencedbymostofthesestrengthenedbeamswasacon-siderablelossinbeamductility.Anexaminationoftheload-deflectionbehaviorofthebeams,however,showedthatthemajorityofthegainedincreaseinloadwasexperiencedaf-tertheyieldofthesteelreinforcement.Inotherwords,asignificantincreaseinultimateloadwasexperiencedwithoutmuchincreaseinyieldload.Hence,asignificantincreaseinservicelevelloadscouldhardlybegained.Apartfromtheconditionoftheconcreteelementbeforestrengthening,thesteelreinforcementcontributessignificantlytotheflexuralresponseofthestrengthenedbeam.Unfortunately,availableFRPstrengtheningmaterialshaveabehaviorthatisdifferentfromsteel.AlthoughFRPmaterialshavehighstrengths,mostofthemstretchtorelativelyhighstrainvaluesbeforeprovidingtheirfullstrength.BecausesteelhasarelativelylowyieldstrainvaluewhencomparedwiththeultimatestrainsofmostoftheFRPmaterials,thecontri-butionofboththesteelandthestrengtheningFRPmaterialsdifferwiththedeformationofthestrengthenedelement.Asaresult,steelreinforcementmayyieldbeforethestrengthenedelementgainsanymeasurableloadincrease.SomedesignersplaceagreaterFRPcrosssection,whichgenerallyincreasesthecostofthestrengthening,toprovideameasurablecontri-bution,evenwhendeformationsarelimited(beforetheyieldofsteel).Debondingofthestrengtheningmaterialfromthesurfaceoftheconcrete,however,ismorelikelytohappeninthesecasesduetohigherstressconcentrations.Debondingisoneofthenondesiredbrittlefailuresinvolvedwiththistechniqueofstrengthening.Althoughusingsomespeciallow-strainfiberssuchasultra-high-moduluscarbonfibersmayappeartobeasolution,itwouldresultinbrittlefailuresduetothefailureoffibers.Theobjectiveofthispaperistointroduceanewpseudo-ductileFRPfabricthathasalowstrainatyieldsothatithasthepotentialtoyieldsimultaneouslywiththesteelreinforcement,yetprovidethedesiredstrengtheninglevel.RESEARCHSIGNIFICANCEFRPshavebeenincreasinglyusedasmaterialsforrehabil-itatingandstrengtheningreinforcedconcretestructures.CurrentlyavailableFRPmaterials,however,lacktheductilityandhavedissimilarbehaviorstosteelreinforcement.Asaresult,thestrengthenedbeamsmayexhibitareducedductility,lackthedesiredstrengtheninglevel,orboth.Thisstudypresentsaninnovativepseudo-ductileFRPstrengtheningfabric.ThefabricprovidesmeasurablyhigheryieldloadsforthestrengthenedbeamsandhelpstoavoidthelossofductilitythatiscommonwiththeuseofcurrentlyavailableFRP.DEVELOPMENTOFHYBRIDFABRICToovercomethedrawbacksmentionedpreviously,aductileFRPmaterialwithlowyieldstrainvalueisneeded.Titleno.99-S71StrengtheningofConcreteBeamsUsingInnovativeDuctileFiber-ReinforcedPolymerFabricbyNabilF.Grace,GeorgeAbdel-Sayed,andWaelF.Ragheb693ACIStructuralJournal/September-October2002LiteraturereviewonhybridizationTodevelopthismaterial,hybridizationfordifferentfiberswasconsidered.Hybridizationofmorethanonetypeoffibrousmaterialswastheinterestofmanymaterialsscienceresearchers.Mostoftheirworkwasconcernedwithcombiningtwotypesoffiberstoenhancethemechanicalpropertiesofeithertypeactingaloneandtoreducethecost.ThishasbeenreportedinseveralpublicationssuchasBunsellandHarris(1974),Philips(1976),MandersandBader(1981),ChowandKelly(1980),andFukudaandChow(1981).HybridizationinterestedstructuralengineersasatooltoovercometheproblemofalackofductilityinFRPreinforcingbars.Nanni,Henneke,andOkamoto(1994)studiedbarsofbraidedaramidfibersaroundasteelcore.TamuzsandTepfers(1995)reportedexperimentalinvestigationsforhybridfiberbarsusingdifferentcombinationsofcarbonandaramidfibers.Somboonsong,Frank,andHarris(1998)developedahybridFRPreinforcingbarusingbraidedaramidfibersaroundacarbonfibercore.Harris,Somboonsong,andFrank(1998)usedthesebarsinreinforcingconcretebeamstoachievethegeneralload-deflectionbehaviorofconcretebeamsreinforcedwithconventionalsteel.DesignconceptandmaterialsTogenerateductility,ahybridizationtechniqueofdifferenttypesoffibershasbeenimplemented.Threefibershavebeenselectedwithadifferentmagnitudeofelongationsatfailure.Figure1showsthestress-straincurvesintensionfortheselectedcompositefibers,andTable1showstheirmechanicalproperties.Thetechniqueisbasedoncombiningthesefiberstogetherandcontrollingthemixtureratiosothatwhentheyareloadedtogetherintension,thefiberswiththelowestelongation(LE)failfirst,allowingastrainrelaxation(anincreaseinstrainwithoutanincreaseinloadforthehybrid).Theremaininghigh-elongation(HE)fibersareproportionedtosustainthetotalloaduptofailure.ThestrainvalueatfailureoftheLEfiberspresentsthevalueoftheyield-equivalentstrainofthehybrid,whiletheHEfiberstrainatfailurepresentsthevalueofultimatestrain.TheloadcorrespondingtofailureofLEfiberspresentstheyield-equivalentloadvalue,andthemaximumloadcarriedbytheHEfibersistheultimateloadvalue.Ultra-high-moduluscarbonfibers(CarbonNo.1)havebeenusedasLEfiberstohaveaslowastrainaspossible,butnotlessthantheyieldstrainofsteel(approximately0.2%forGrade60steel).Ontheotherhand,E-glassfiberswereusedasHEfiberstoprovideashighastrainaspossibletoproduceahigh-ductilityindex(theratiobetweendeformationatfailureanddeformationatyield).High-moduluscarbonfibers(CarbonNo.2)wereselectedasmedium-elongation(ME)fiberstominimizethepossibleloaddropduringthestrainrelaxationthatoccursafterfailureoftheLEfibers,andalsotoprovideagradualloadtransitionfromtheLEfiberstotheHEfibers.Basedonthisconcept,auniaxialfabricwasfabricatedandtestedtocompareitsbehaviorintensionwiththetheoreticalpredictedloadingbehavior.Thetheoreticalbehaviorisbasedontheruleofmixtures,inwhichtheaxialstiffnessofthehybridiscalculatedbyasummationoftherelativestiffnessofeachofitscomponents.Thefabricwasmanufacturedbycombiningdifferentfibersasadjacentyarnsandimpregnatingtheminsideamoldbyanepoxyresin.Figure2showsaphotoofoneofthefabricatedsamples.Wovenglassfibertabswereprovidedatbothendsofthetestcouponstoeliminatestressconcentrationsatendfixturesduringtesting.Thecouponshadathicknessof2mm(0.08in.)andawidthof25.4mmACImemberNabilF.GraceisaprofessorandChairoftheStructuralTestingCenter,DepartmentofCivilEngineering,LawrenceTechnologicalUniversity,Southfield,Mich.HeisamemberofACICommittee440,FiberReinforcedPolymerReinforcement;andJointACI-ASCECommittee343,ConcreteBridgeDesign.Hisresearchinterestsincludetheuseoffiber-reinforcedpolymerinreinforcedandprestressedconcretestructures.GeorgeAbdel-SayedisProfessorEmeritusintheDepartmentofCivilandEnvi-ronmentalEngineering,UniversityofWindsor,Windsor,Ontario,Canada.Hisresearchinterestsincludesoil-structureinteraction.WaelF.RaghebisaresearchassistantintheDepartmentofCivilEngineeringatLawrenceTechnologicalUniversity.HeisaPhDcandidateintheDepartmentofCivilandEnvironmentalEngineering,UniversityofWindsor,Windsor,Ontario,Canada.Fig.1Stress-strainbehaviorofcompositefibersandsteelreinforcingbars.*Compositepropertiesarebasedon60%fibervolumefraction.Table1Mechanicalpropertiesofcompositefibers*FibermaterialDescriptionModulusofelasticity,GPa(Msi)Tensilestrength,MPa(ksi)Failurestrain,%CarbonNo.1Ultra-high-moduluscarbonfibers379(55)1324(192)0.35CarbonNo.2High-moduluscarbonfibers231(33.5)2413(350)0.9to1.0GlassE-glassfibers48(7)1034(150)2.1Fig.2Testsamplefordevelopeduniaxialhybridfabric.Fig.3Resultsoftensiletestsfordevelopedhybridfabric.694ACIStructuralJournal/September-October2002(1in.)andweretestedintensionaccordingtoASTMD3039specifications.Theaverageload-straincurveforfourtestedsamplesisshowninFig.3togetherwiththetheoreticalprediction.Itshouldbenotedthatthebehaviorislinearuptoastrainof0.35%,whentheLEfibersstartedtofail.Atthispoint,thestrainincreasedatafasterratethantheload.Whenthestrainreached0.90%,theMEfibersstartedtofail,resultinginanadditionalincreaseinstrainwithoutasignificantincreaseinload,uptothetotalfailureofthecouponbyfailureoftheHEfibers.Ayield-equivalentload(thefirstpointontheload-straincurvewherethebehaviorbecomesnonlinear)of0.46kN/mmwidth(2.6kips/in.)andanultimateloadof0.78kN/mm(4.4kips/in.)areobserved.BEAMTESTSBeamdetailsThirteenreinforcedconcretebeamswithcross-sectionaldimensionsof152x254mm(6x10in.)andlengthsof2744mm(108in.)werecast.TheflexurereinforcementofthebeamsconsistedoftwoNo.5(16mm)tensionbarsnearthebottom,andtwoNo.3(9.5mm)compressionbarsnearthetop.Toavoidshearfailure,thebeamswereover-reinforcedforshearwithNo.3(9.5mm)closedstirrupsspacedat102mm(4.0in.).Fivebeamswereformedwithroundedcornersof25mm(1in.)radiustofacilitatetheinstallationofthestrengtheningmaterialontheirsidesandbottomfaceswithoutstressconcentrations.Figure4showsthebeamdimensions,reinforcementdetails,supportlocations,andlocationofloadingpoints.ThesteelusedwasGrade60withayieldstrengthof415MPa(60,000psi),whiletheconcretecompressivestrengthatthetimeoftestingthebeamswas55.2MPa(8000psi).StrengtheningmaterialsThedevelopedhybridfabricwasusedtostrengtheneightbeams.Twodifferentthicknessesoffabricwereused.Thefirst(H-system,t=1.0mm)hadathicknessof1.0mm(0.04in.),andthesecond(H-system,t=1.5mm)hadathicknessof1.5mm(0.06in.).Fourotherbeamswerestrengthenedwiththreecurrentlyavailablecarbonfiberstrengtheningmaterials:1)auniaxialcarbonfibersheetwithanultimateloadof0.34kN/mm(1.95kips/in.);2)twolayersofauniaxialcarbonfiberfabricwithanultimateloadof1.31kN/mm(7.5kips/in.)forthetwolayerscombined;and3)apultrudedcarbonfiberplatewithanultimateloadof2.8kN/mm(16kips/in.).Thetestedload-straindiagramsforFig.4Detailsoftestbeams.Fig.5Comparisonbetweencarbonfiberplate,fabric,sheet,anddevelopedhybridfabric(H-System).ACIStructuralJournal/September-October2002695allthesematerialsareshowninFig.5.Table2showsthepropertiesofthestrengtheningmaterials,includingthedevelopedfabric.AdhesivesForthehybridfabric,anepoxyresin(EpoxyA)wasusedtoimpregnatethefibersandasanadhesivebetweenthefabricandtheconcretesurface.Thisepoxyhadanultimatestrainof4.4%toensurethatitwouldnotfailbeforethefailureofthefibers.Forthebeamsstrengthenedwithcarbonfibersheets,plates,andfabric,anepoxyresinwithanultimatestrainof2.0%wasused(EpoxyB).ThemechanicalpropertiesoftheadhesivesprovidedbytheirmanufacturesareshowninTable3.StrengtheningThebeambottomfacesandsidesweresandblastedtoroughenthesurface.Thebeamswerethencleanedwithacetonetoremovedirt.Twostrengtheningconfigurationswereused:1)strengtheningmaterialonthebottomfaceofthebeamonly(BeamGroupA);and2)strengtheningmaterialonthebottomfaceandextendedup152mm(6in.)onbothsidestocoverapproximatelyalltheflexuraltensionportionsofthebeam(BeamGroupB).Thestrengtheningwasinstalledfor2.24m(88in.),centeredalongthelengthofthebeam.Theepoxywasallowedtocureforatleast2weeksbeforethebeamsweretested.Forthebeamsstrengthenedwiththedevelopedhybridfabric(H-system),twobeamswerefabricatedandtestedforeachconfigurationtoverifytheresults.Table4summarizesthetestbeams.InstrumentationTheFRPstrainatmidspanwasmeasuredbythreestraingageslocatedatthebottomfaceofthebeam.ThesteeltensilestrainwasmeasuredbymonitoringthestrainonthesidesurfaceofthebeamatreinforcingbarlevelusingaDEMEC(detachablemechanicalgage)withgagepointsforBeamGroupA,whilestraingageswereusedforBeamGroupB.Themidspandeflectionwasmeasuredusingastringpoten-tiometer.Thebeamswereloadedusingahydrau

温馨提示

  • 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
  • 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
  • 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
  • 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
  • 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
  • 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
  • 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。

评论

0/150

提交评论