桥梁工程毕业设计外文翻译Word格式文档下载.docx
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桥梁工程毕业设计外文翻译Word格式文档下载.docx
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Thispaperpresentsareviewoftheprogressoftheresearchandengineeringpracticeofassessmentandrepairoffire-damagedRChighwaybridges,basedonwhichexistingandpressingproblemsoftheevaluationmethodarepointedout.Atlast,Prospectforthedevelopmentofassessmentandrepairoffire-damagedhighwaybridgesisalsoproposed.
Keywords:
firedamage;
assessment;
repairtechniques;
RCstructure;
bridge
1Preface
Firescancausegreatstructuraldamagetobridgesandmajordisruptiontohighwayoperations.Theseincidentsstemprimarilyfromvehicleaccident(oftenoiltanker)fires,bridgesmightalsobedamagedbyfiresinadjacentfacilitiesandfromothercauses.Quiteafewofthem,
thoughrarelyhappened,leadtoseverestructuraldamageorcollapseandcasualty.
OnJune2,2008,firedisasterbrokeoutunderthe18thspanofNanjingYangtzeRiverBridgeandlastedforapproximate75min.Duringthefire’sdevelopmentandextinguishment,thestructureexperiencedthesharpriseandfallintemperaturecausingseveredamagetofire-strickensegments.OnApril29,2007,agasolinetankeroverturnedontheconnectorfromInterstate8OtoInterstate880inCalifornia.Theintenseheatfromthesubsequentfuelspillandfireweakenedthestee1underbellyoftheelevatedroadway,collapsingapproximately165feetofthiselevatedroadwayontoasectionofI—880below.OnMarch25,2004,Connecticut,UnitedStates,atankertruckcarryingfuelswervedtoavoidacarandoverturned,dumping8000gallonsofhomeheatingoilontotheHowardAvenueoverpass.Theconsequenttoweringinfernomeltedthebridgestructureandcausedthesouthboundlanestosagseveralfeet
Undocumentednumberofbridgefiresoccurringthroughouttheworldeachyearcausevaryingdegreesofdisruption,repairactions,andmaintenancecost.Althoughfirescauseddamagetothebridgestructures,somebridgescontinuetofunctionafterproperrepairandretrofit.Stillinsomesituationstheyhavetoberepairedforthecauseoftrafficpressureeventhoughsupposedtobedismantledandreconstructed.However,inothercases,structuresareseverelydamagedinthefiredisasterandfailtofunctionevenafterrepair,orthecostsofrepairandretrofitoverweightheirreconstructioncostsoverwhelminglyeveniftheyarerepairable,underwhichsituationreconstructionservesasapreferableoption.Thereforein—situinvestigationandnecessarytestsandanalysesshouldbeconductedtomakecomprehensiveassessmentoftheresidualmechanicalpropertiesandworkingstatusesafterfireandtoevaluatethedegreesofdamageofmembersandstructures,inreferencetowhichdecisionsaremadetodeterminewhetherFiredamagedstructuresshouldberepairedordismantledandreconstructed.Urgentneedfromengineeringpracticehighlightedthenecessitytounderstandthesusceptibilityandseverityoftheseincidentsaswel1astoreviewavailableinformationonmitigationstrategies,damageassessments,andrepairtechniques.
2ProgressinResearchandEngineeringPractice
2.1ProcessesofAssessmentandRepairofFiredamagedBridgeStructure
InChinaandmostcountriesintheworld,mosthighwaybridgesarebuiltinRCstructure.AndthepracticeoftheassessmentandrepairtechniquesofbridgestructureafterfiredirectlyrefertothatofRCstructure,which,todate,domesticandforeignscholarshavemadegreatamountofresearchon,withtheirtheoriesandpracticesbeingincreasinglymature.Asfortheassessmentandrepairoffire-damagedreinforcedconcretestructures,therearetwomainstreamassessmentprocessesinworld.
CountriesincludingUnitedStates,UnitedKingdomandJapanadopttheassessmentprocessstipulatedbyTheBritishConcreteSociety.Thisprocessgratestheseverityoffiredamageofconcretestructureintofourdegreesaccordingtothedeflection,damagedepth,crackingwidth,color,andloadingcapacityvariationoffire-damagedstructuresandadoptfourcorrespondingstrategies(includingdemolish,strengthenaftersafetymeasures,strengthen.andstrengthenindamagedsegments)todealwiththemaccordingly.Ingeneral,thisprocessisaqualitativemethodandconsidered,however,notquantityenough.
InChineseMainlandandTaiwan,theprevailingasassessmentandrepairprocessoffiredamagedincorporatesfollowingsteps:
Incomparisonthisprocessismoredetailed.
(1)ConductIn-situinspections,measurements,andtestsincludingcolorobservation,concreteobservation,degreeofrebarexposureobservation,crackingmeasurement,deflectionmeasurement,variousdestructiveandnondestructivetestmethodsasgroundsforassessmentoffire—damagedstructures.Inassessmentofthepost-firemechanicalpropertiesoffire—damagedstructures,historicalhighesttemperatureandtemperaturedistributionofstructureduringthefireserveasdecisivefactors.Thecommonmethodstodeterminethemincorporatepetrographicanalysis,ultrasonicmethod,Reboundmethod,IgnitionLossmethod,coretest,andcolorobservationmethod
(2)calculatetodeterminewhetherthefire-damagedstructurecanmeetthedemandofstrengthanddeflectionunderworkingloadsafterfireusingmechanicalpropertiesofrebarandconcretebeforeandafterfirebasedonthehistoricalhighestandtemperaturedistributionofstructuresobtainedfromstepone.Therearetwomainmethodstoevaluatethepost-fireperformanceoffire-damagedstructures:
FEMmethodandRevisedClassicMethod.
(3)Onthebasisoftestandcalculationresultsobtainedfromsteptwo,takecorrespondingrepairstrategiesandparticularmethodstostrengthenthefire-damagedstructures.
2.2RepairTechniques
Fortherepairoffire—damagedbridge,properrepairmethodsshouldbetakenaccordingtothedegreeandrangeofthestructure’sdamage.Meanwhilethesafetyandeconomyoftherepairmethodsshouldbeconcernedwithbyavoidingdestructingtheoriginalstructure,preservingthevaluablestructuralmembers,andminimizingunnecessarydemolishmentandreconstruction。
Commonrepairtechniquesarelistedasfollows.
(1)Fire-damagedconcreteReplacement
Thereplacementoffire—damagedconcreteisthemostcommontechniqueindamagedconcreterepair.Iftheconcretestructureisdamagedonlywithintheconcretecover,itispreferabletoremovethefire—damagedconcretefromthestructuremakingtherebarexposedandtomakeuptheremovedpartbymeansofrecastingorconcretespraying.Ifthedisplacementofthestructureexceedsthecontrolledvalueortheembeddedrebarisbuckled,thedamagedstructureshouldbeotherwisehandled。
(2)CFRPstrengthening
CFRPmaterialshavestrongtensilestrengthandelasticityaswellasexcellentworkabilityanddurabilityandarewidelyappliedinengineeringpracticeinrecentyears.CFRPmaterialsareusedtoboosttheloadingcapacitybyadheringthemtotheedgeoftensileregiontoreplacethereinforcedrebar.CFRPareespeciallysuitablefortheprojectscallingforboostofloadingcapacitywhilenoextraweightisallowed.
(3)StructuralmemberReplacement
Forslabbridgesandgirderbridges,thedecksofthebridgearemadeofparallelgirdersorthickslabs.Onconditionthatpartofstructuralmemberisseverelydamagedinthefiresothatit’sbeyondrepairortherepaircostoverweighanewone,itispreferabletoreplacethe
damagedspanswithnewgirdersorslabs.Thoughappearstoberelativelyhighincost,thismethodservesasreliableandeffectivewayinengineeringpractice
2.3CaseStudyofAssessmentandRepairTechniquesoffire-damagedbridges
Somedomesticandforeignscholarshaveconductedaseriesofstudiesontheinspection,assessment,andrepairtechniquesoffiredamagedbridgesintheengineeringpracticebydifferentassessmentstandardsandprocessesonthecase—by—casebasisusingavarietyoffieldand
laboratoryevaluationmethods,includingbothdestructiveandnondestructivetesting
Literatureemployedvisualinspectionandmaterialtestingincludingcompressivestrengthtestingandpetrographicanalysis(pastedepth,microcracking,colorchange)onafire-damagedbridge,basedonwhich1oadratinganalysiswasperformedusingreducedgirderanddecksections.Literaturemadequalitativesafetyevaluationontwofire-damagedbridgestructuresusingthereboundmethod,coretests,carbonizationdepthmeasurement,concretecovermeasurement,deflectionmeasurement,andappearanceobservation.Literatureusethecombinationofultrasonicmethodandreboundmethodtodeterminethehistoricalhighesttemperatureofstructuresinfire,basedonwhichstiffnessandstrengthoftwofiredamagedstructuresaredeterminedtomakesafetyevaluationsonthem.AndthenCFRPandstructuraladhensiveareusedtostrengthenthefire—damagedsegmentsrespectively.Literaturemadeasafetyevaluationonaprestressedreinforcedconcreteslabbridge,thefire—directly—strickensegmentsofwhichareseverelyspalledandcarbonizedwithembeddedrebarsandprestressedstrandsexposed.Itsrubberisolatorswerealsohighlycarbonized.Theresearchertookthecoretestsandinferredthatlocalsegmentsoftheslabswereseverelydamagedandtheprestresshadbeenlost.Meanwhile,theresearcherconductedaseriesofdynamictestsonthedamagedbridgeandpresumedthatthevariationofthecomprehensiveperformanceofthebridgestructureafterfirewasinsignificantinreferencetotheresultsofthedynamictests.Theresearcherproposedtoreplacetheseverelydamagedslabsfromtheperspectiveofdurabilityandsafety.Literaturemadethedamageassessmentandrepairworkonafire-damagedT-shapedprestressedbeambridge.Thefiredisasterwasderivedfromtheleakageofaoiltankerandthentheburningoilwasspreadtotheunderbellyofthebridge.
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