桥梁毕业设计外文翻译混凝土桥的结构处理工具.docx

桥梁毕业设计外文翻译混凝土桥的结构处理工具.docx

《桥梁毕业设计外文翻译混凝土桥的结构处理工具.docx》由会员分享，可在线阅读，更多相关《桥梁毕业设计外文翻译混凝土桥的结构处理工具.docx（7页珍藏版）》请在冰豆网上搜索。

桥梁毕业设计外文翻译混凝土桥的结构处理工具

第二部分英文翻译

Reliabilityanalysis:

astructuresmanagementtoolforconcretebridges

Reinforcedconcretestructuresaresusceptibletoavarietyofdeteriorationmechanisms,includingalkali-thawactionandchlorideingress.Substantialresearchhasbeenundertakeninrelationtothesemechanismsandotherproblems.Thishasparticularlybeenthecaseoverthelast20yearsorso,wheretheobjectivehasbeentoidentifycauses,consequencesanddevelopremediationstrategies.Thishasimprovedunderstandingoflong-termbehaviourofreinforcedconcreteandresultedinthedevelopmentoftechniquestoincreasedeteriorationresistance.

Atpresent,themostcommonapproachistoactafteraproblemhasbeenidentified,knownasre-activemaintenance.Thismaynotbethemosteconomicsolutionsince,inmanycases,maintenanceismorecostlythanpreventativetreatments.However,ownersareoftenreluctanttopayforpreventativetreatmentsbeforedeteriorationisapparent.Earlyapplicationoftreatmentsmaynotbetheoptimalsolutioninthelongrun.Integrateddeteriorationandperformancepredictionmodelingisessentialtopro-activelyplanandprioritiseinspection,testingandmaintenance.Thisbecomesincreasinglyimportantasinfrastructureagesandjustificationformaintenancefundingbecomesincreasinglycritical.

Performanceassessmentcanbeachievedthroughsurveys,testingandformalcalculations,ideallybasedonsitedatathatrepresent,asaccuratelyaspossible,thestateofthestructure.Byintegratingpredictivedeteriorationmodelswithassessmenttoolsandperformancecriteria（atelement,structureorgrouplevel）itbecomespossibletobasethemaintenanceregimeontime-dependentperformanceprofiles.Thisisparticularlyrelevantinthecontextofwhole-wifecostingprocedures.

Substantialresearchhasbeenundertakeninrelationtothesemechanismsandotherproblems.Thishasparticularlybeenthecaseoverthelast20yearsorso,wheretheobjectivehasbeentoidentifycauses,consequencesanddevelopremediationstrategies.Thishasimprovedunderstandingoflong-termbehaviourofreinforcedconcreteandresultedinthedevelopmentoftechniquestoincreasedeteriorationresistance.

Atpresent,themostcommonapproachistoactafteraproblemhasbeenidentified,knownasre-activemaintenance.Thismaynotbethemosteconomicsolutionsince,inmanycases,maintenanceismorecostlythanpreventativetreatments.However,ownersareoftenreluctanttopayforpreventativetreatmentsbeforedeteriorationisapparent.Earlyapplicationoftreatmentsmaynotbetheoptimalsolutioninthelongrun.Integrateddeteriorationandperformancepredictionmodelingisessentialtopro-activelyplanandprioritiseinspection,testingandmaintenance.Thisbecomesincreasinglyimportantasinfrastructureagesandjustificationformaintenancefundingbecomesincreasinglycritical.

Reliabilityanalysishasemergedasanimportanttoolinthismulti-objectivemanagementprocess,whichmusttakeintoaccountsafety,functionalityandsustainabilitycriteria.Insimpleterms,thereliabilityofastructureorasystemistheprobabilityofachievingaparticularperformancelevel.Probabilityorlikelihoodistheappropriatemeasure,sinceallengineeringsystemsaresusceptibletouncertainties,arisingfromrandomphenomenaandincompleteknowledge.Reliabilityanalysisinstructuralengineeringenablesquantificationofuncertaintiesassociatedwithloading,materials,deterioration,modelingandotherfactors.Theseareintegratedintoamethodthatestimatestheprobabilityofreachingthespecifiedperformancelevelduringtheservicelifeofastructure.Themethodisincreasinglybeingusedinbridgeengineering,bothforcalibrationofsafetylevelsincodesandstandardsandimprovingandrefiningassessmentmethodologies.Thepurposeofthisarticleistooutlineitsapplicationinmanagingbridgessusceptibletodeterioration.

Althoughdataformanydeteriorationvariablescanbederivedfromlaboratorystudies,thereisanabsenceofsimilardatarealstructures.Animportantfeatureofthemodelisthefacilitytomodifyinitialpredictions,basedonpublished（knownas‘prior’）data,usinginformationanddataobtaineddirectlyfromtheactualstructures.Reliabilityanalysisisappropriateforthispursoseasifitcanreadilyincorporateadditionaldata,updatingtheprobabilityofreachingaperformancetarget.Theconceptisanalogoustoupdatingtheprobabilityofarrivingontimewhilstonatrain,havingjustobtainsomeextrainformationregardingtheoperatingconditionsahead.

Typicalresultsproducedbytheprobabilisticdeteriorationmodelforacrossbeamchlorideexposurezone,similartothedelaminatedareashowninFigure3,areshowninFigure4.Assumingathresholdof40%initiationisspecifiedforthefirstinspection,themodelsuggeststhatitshouldbeundertakenaftereightyears.Assumingthatinspectionindicatessignificantlylesscorrosioninitiation（e.g.onlyabout10%）andattributed,throughsiteinvestigations,toconcretecoverbeinghigherthanexpected,arevisedpredictionoftheperformanceprofilemaybegenerated.Thebridgemanagementactionsmaythenbealteredaccordingly.

Figure5illustrateshowalimitstateprofileforthiszonechangeswithassumedconditions.Thedeteriorationmodelhasbeenintegratedwithbondlimitstateequations.Thus,assumingthatthecomponenthasatargetnominalprobabilityoffailureof1×10-5peryear,profile1suggestsalifetimeofonly17to18years,whereasProfile2suggests30to31years.Bothareshortlifetimeswhencomparedwiththenormallifeexpectancyofbridges.However,initialconditionsrelatingtotheseresultsassumethatthedeckjointhasfailedfromtheoutset.Alternatively,theexpressionsformodellingbondstrengthmaybeover-conservative,astheyweredevelopedforintactstructures.

Substantialresearchhasbeenundertakeninrelationtothesemechanismsandotherproblems.Thishasparticularlybeenthecaseoverthelast20yearsorso,wheretheobjectivehasbeentoidentifycauses,consequencesanddevelopremediationstrategies.Thishasimprovedunderstandingoflong-termbehaviourofreinforcedconcreteandresultedinthedevelopmentoftechniquestoincreasedeteriorationresistance.

Atpresent,themostcommonapproachistoactafteraproblemhasbeenidentified,knownasre-activemaintenance.Thismaynotbethemosteconomicsolutionsince,inmanycases,maintenanceismorecostlythanpreventativetreatments.However,ownersareoftenreluctanttopayforpreventativetreatmentsbeforedeteriorationisapparent.Earlyapplicationoftreatmentsmaynotbetheoptimalsolutioninthelongrun.Integrateddeteriorationandperformancepredictionmodelingisessentialtopro-activelyplanandprioritiseinspection,testingandmaintenance.Thisbecomesincreasinglyimportantasinfrastructureagesandjustificationformaintenancefundingbecomesincreasinglycritical.

Bridgeperformancecriteria

CurrentUKassessmentcodesareconcernedwithultimatelimitstates（ULS）anddonotexplicitlyrequirecheckingofserviceabilitylimitstates（ULS）.ItisassumedthatanexistingstructurehasexperiencedSLSloadsduringitslife.However,thewidelyacceptedSLScriteriaofdeflectionandcrackingdonotfullytakeintoaccounttheproblemsposedbydeterioration.Deterioration-basedcriteriasuchasruststaining,delaminationandspallingneedtobeconsideredbecausetheyclearlyinfluencebridgeperformance,bothfunctionalandfinancial.Theseoftenprovethedominantfactorwithregardtobridgemanagementstrategy.

Byexplicitlyconsideringandspecifyingperformancelevels,theengineerisawareoftheimportantdeteriorationindicatorsinordertoestablishtheinspectionandmaintenanceregimefortheparticularstructure/member.Theseperformancelevelsmaychangeovertime,duetochangesinfunction,loading,structureimportanceetc.forexample,therelationshipbetweenactualandrequiredperformanceisconceptualizedbythediagramshowninFigure1.Thus,reliabilityanalysismaybeusedtoformulatetheprobabilitythatperformancewillexceedthatrequired,therebyestimatingthereliabilityofthestructure.Theperformancemeasurecanberelatedtosafety,functionalityoranyotherappropriatecriterion.

Modelingchloride-induceddeterioration

Thisparticularprojectconcentratedononespecificareaofreinforcedconcretedeterioration,specificallyarisingfromchlorideingress.Chloridesarepresentinde-icingsaltsusedintheUKduringwinter.Chlorideionsmigratethoughtheconcrete,e.g.byabsorptionanddiffusion.Undersuitableconditions,theyinitiatereinforcementbarcorrosion.Thecorrosionmechanismproducesrust.Theincreasedvolumeofthemetal,duetotherust,leadstocracking,delaminationandspallingoftheconcretecover.Thisresultsinmorerapidandextensivereinforcementcorrosion.

Reinforcedconcretebridgeelementslocatedbelowexpansionjointsareparticularlysusceptibletochlorideattackifthejointfails.HighwayviaductsintheUKtypicallyconsistofareinforcedconcretecrossbeamdirectlylocatedbelowtheexpansionjoint,（seeFigure2）.Manycrossbeamshavesufferedseverereinforcementcorrosion,delaminationandspalling.AtypicalexampleisshowninFigure3,wherethereinforcementcoveroverthecrossbeamhasdelaminated.

Aprobabilisticdeteriorationmodelforreinforcedconcretebridgecomponentswasdeveloped,takingintoaccountthecharacteristicsofthesestructuresandtheirenvironment.Itassumesthatbothdiffusionandabsorptionplayapartinchlotidemigrationthroughtheconcrete,thevariabilityinthequantityofde