土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究.docx

土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究.docx

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土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究

中文2630字

ANEXPERIMENTALSTUDYONFLEXURALBEHAVIOROFRCBEAMS

STRENGTHENEDWITHNSMREINFORCEMENT

Woo-TaiJUNG1,Young-HwanPARK2,Jong-Sup

ABSTRACT:

ThisstudypresentstheresultsofexperimentsperformedonRC（ReinforcedConcrete）beamsstrengthenedwithNSM（NearSurfaceMounted）reinforcement.Atotalof6specimenshavebeentested.ThespecimenscanbeclassifiedintoEBR（ExternallyBondedReinforcement）specimenandNSMreinforcementsspecimens.TwoNSMspecimenswithspacevariableswerestrengthenedwith2CFRP（CarbonFiberReinforcedPolymer）strips.ExperimentalresultsrevealedthatNSMspecimensusedCFRPreinforcementsmoreefficientlythantheEBRspecimens.EvenifCFRPcrosssectionareasofNSMspecimenshave30%,50%ofEBRSpecimen,thestrengtheningeffectofNSMspecimensissuperiortoEBRspecimen.NSMspecimenswithspacevariablesshowedthatthstrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedascomparedtothespecimenwithwidespaceu

KEYWORDS:

carbonfiberreinforcedpolymer,externallybondedCFRPreinforcements,nearsurfacemountedCFRPreinforcements,strengthening

1.INTRODUCTION

AmongthevariousstrengtheningtechniquesthathavebeendevelopedandappliedtostrengthendeterioratedRCstructures,anumberofapplicationsusingFRPreinforcementshavesignificantlyincreasedrecently.FRPreinforcementsarebondedtoconcretesurfacesbyadhesivesbutfrequentlyexperiencedebondingfailureattheinterfacebetweenFRPreinforcementsandconcrete.Mostresearch,todate,hasfocusedoninvestigatingthestrengtheningeffectsandfailuremodesofEBRsystem

TheproblemofprematurefailureofEBRsystemmaybesolvedbyincreasingtheinterfacebetweenFRPandconcrete.Usingthisprinciple,theNSMsystemhasbeenintroducedrecently.TheNSMsystemforconcretestructureusingsteelreinforcementalreadybeganin1940s.However,thecorrosionofthesteelreinforcementandthepoorbondingperformanceofthegroutingmateriallargelyimpaireditsapplication.ThedevelopmentofimprovedepoxyandtheadoptionofFRPreinforcementofferedtheopportunitytoimplementNSMsystem（HassanandRizkalla2003;TäljstenandCarolin2001）.Becauseoftheirlightweight,easeofinstallation,minimallaborcostsandsiteconstraints,highstrength-to-weightratios,anddurability,FRPrepairsystemscanprovideaneconomicallyviablealternativetotraditionalrepairsystemsandmaterials（Mirmiranetal.2004）.RizkallaandHassan（2002）havecomparedEBRandNSMsystemintermsofcost,includingcostsofmaterialsandlabor,

andstrengtheningeffect.TheyconcludedthattheNSMsystemwasmorecost-effectivethantheEBRsystemusingCFRPstrips.

ThisexperimentalstudyinvestigatestheapplicabilityandstrengtheningperformancesofNSMusingCFRPstrips.Forcomparison,flexuraltestsonRCbeamsstrengthenedbyEBRandbyNSMhavebeenperformed.Inaddition,specimenswithspacevariableshavebeentestedtocomparethestrengtheningperformancebycrosssectionwithwideandnarrowspace.

2.EXPERIMENTALPROGRAM

2.1MANUFACTUREOFSPECIMENS

Atotalof6specimensofsimplysupportedRCbeamswithspanof3mhavebeencast.Thedetailsandcross-sectionofthespecimensareillustratedinFigure1.Aconcretewithcompressivestrengthof31.3MPaat28dayshasbeenused.SteelreinforcementsD10（φ9.53mm）ofSD40havebeenarrangedwithsteelratioof0.0041andalayerofthreeD13（φ12.7mm）hasbeenarrangedascompressionreinforcements.ShearreinforcementsofD10havebeenlocatedevery10cmintheshearzonetoavoidshearfailure.Table1summarizesthematerialpropertiesusedforthetestbeams.

2.2EXPERIMENTALPARAMETERS

Table2liststheexperimentalparameters.Thecontrolspecimen,anunstrengthenedspecimen,hasbeencasttocomparethestrengtheningperformancesofthevarioussystems.CPL-50-BOND,EBRspecimen,hasbeenstrengthenedwithCFRPstrip.Theremaining4specimenswerestrengthenedwithNSMCFRPstrips.AmongthespecimensstrengthenedwithNSMreinforcements,anembedding64depthofNSM-PL-15andNSM-PL-25is15mmand25mm,respectively.AspacebetweengroovesofNSM-PL-25*2andNSM-PL-2Sis60mmand120mm,respectively.Thestrengthenedlengthofallthespecimenshasbeenfixedto2,700mm

2.3INSTALLATIONOFTHEFRPREINFORCEMENTS

Figure2showsthedetailsofcross-sectionsofthespecimens.ThestrengtheningprocessofEBRspecimen（CPL-50-BOND）wasproceededbythesurfacetreatmentusingagrinder,followedbythebondingoftheCFRPstrip.Thestrengthenedbeamswerecuredatambienttemperaturefor7daysforthecuringofepoxyadhesive.TheprocessforNSMstrengtheningprogressedbycuttingthegroovesatthebottomofthebeamsusingagrinder,cleaningthedebris,andembeddingtheCFRPstripafterapplicationoftheadhesive.Thestrengthened

beamswerecuredfor3dayssothattheepoxyadhesiveachievesitsdesignstrength.

2.4LOADINGANDMEASUREMENTMETHODS

Allspecimensweresubjectedto4-pointbendingteststofailurebymeansofUTM（UniversalTestingMachine）withcapacityof980kN.Theloadingwasappliedunderdisplacementcontrolataspeedof0.02mm/secuntilthefirst15mmand0.05mm/secfrom15mmuntilfailure.Themeasurementofalltestdatawasrecordedbyastaticdataloggerandacomputeratintervalsof1second.Electricalresistancestraingaugeswerefixedatmid-spanandL/4tomeasurethestrainofsteelreinforcements.Straingaugestomeasurethestrainofconcretewerelocatedatthetop,5cmand10cmawayfromthetopononesideatmid-span.StraingaugeswerealsoplacedontheFRPreinforcementlocatedatthebottomofthemid-spanandloadedpointstomeasurethestrainaccordingtotheloadingprocess.

3.EXPERIMENTALRESULTS

3.1FAILUREMODES

Beforecracking,allthestrengthenedspecimensexhibitedbendingbehaviorsimilartothe

unstrengthenedspecimen.ThisshowsthattheCFRPreinforcementisunabletocontributetotheincreaseofthestiffnessandstrengthintheelasticdomain.However,aftercracking,thebendingstiffnessandstrengthofthestrengthenedspecimenswereseentoincreasesignificantlyuntilfailurecomparedtotheunstrengthenedspecimens.Examiningthefinalfailure,theunstrengthenedcontrolspecimenpresentedtypicalbendingfailuremodewhichproceedsbytheyieldingofsteelreinforcementfollowedbycompressionfailureofconcrete.ThefailureofCPL-50-BOND,EBRspecimen,beganwiththeseparationofCFRPreinforcementandconcreteatmid-spantoexhibitfinallybrittledebondingfailure（Figure3）.FailureofNSM-PL-15,NSMspecimen,occurredwiththeruptureoftheFRPreinforcement.FailureoftheremainingNSMspecimens（NSM-PL-25,NSM-PL25*2,andNSM-PL-2S）occurredthroughthesimultaneousseparationoftheCFRPreinforcementandepoxyfromconcrete（Figure4,5,and6）.Table3summarizesthefailuremodes.

3.2STRENGTHENINGEFFECT

Figure7plotedtheload-deflectioncurvesofEBRandNSMspecimens.ThespecimenswithEBR,CPL-50-BOND,presentedultimateloadincreasedby30%comparedtotheunstrengthenedspecimen,whileNSMspecimens（NSM-PL-15,NSM-PL-25）increasedtheultimateloadby40to53%.ObservationofFigure7revealsthatevenifCPL-50-BONDwithrelativelylargecross-sectionalareaofCFRPreinforcementdevelopedlargerinitialstiffness,prematuredebondingfailureoccurredbecauseitsbondingareaismuchsmallerthanNSM-PL-15,NSM-PL-25.EBRspecimenbehavedsimilarlytotheunstrengthenedcontrolspecimenafterdebondingfailure.InFigure7,thestiffnessofNSMspecimensbeforeyieldingofsteelreinforcementwassmallerthanthestiffnessdevelopedbyEBRspecimenbecauseNSMspecimenshavethesmallercross-sectionalareaofCFRPreinforcementthanEBRspecimen.Theultimateloadandyieldloadareseentoincreasewiththecross-sectionalareaofNSMreinforcement.ExaminingtheultimatestrainofFRPsummarizedinTable3,themaximumstrainforEBRspecimenappearstoattain30%oftheultimatestrain,and80to100%forNSMspecimens.ThisprovesthattheNSMsystemisutilizingCFRPreinforcementefficiently（2Swiththesamecross-sectionalareaasCPL-50-Bondresentedultimateloadincreasedby95%,90%comparedtotheunstrengthenedspecimen,respectively.Consideringthesamecross-sectionalarea,thestrengtheningeffectofNSMspecimensissuperiortotheEBRspecimen.

InFigure8,NSM-PL-25*2andNSM-PL-2S,NSMspecimenswithspacevariables,showedthatthestrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedby2.5%ascomparedtothespecimenwithwidespace.

4.CONCLUSIONS

PerformancetestshavebeencarriedoutonRCbeamsstrengthenedwithNSMsystems.Thefollowingconclusionswerederivedfromtheexperimentalresults.IthasbeenseenthatNSMspecimensutilizedtheCFRPreinforcementmoreefficientlythantheEBRspecimen.Accordingtothestaticloadingtestresults,thestrengtheningperformanceswereimproved

inNSMspecimenscomparedwithEBRspecimen.However,thespecimensNSM-PL-25,NSM-PL-25*2andNSM-PL-2SfailedbytheseparationoftheCFRPreinforcementsandepoxyadhesivefromtheconcrete.Consequently,itisnecessarytotakesomecountermeasurestopreventdebondingfailureforNSMspecimens.Consideringthesamecross-sectionalarea,thestrengtheningeffectofNSMspecimensissuperiortoEBRspecimen.NSM-PL-25*2andNSM-PL-2S,NSMspecimenswithspacevariables,showedthatthestrengtheningeffectofthespecimenwithnarrowspaceisslightlyincreasedascomparedtothespecimenwithwidespace.

5.REFERENCES

1.Hassan,T.andRizkalla,S.（2003）,InvestigationofBondinConcreteStructuresStrengthenedwithNearSurfaceMountedCarbonFiberReinforcedPolymerStrips”,JournalofComposite