土木工程专业英语带翻译.docx

土木工程专业英语带翻译.docx

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土木工程专业英语带翻译

State-of-the-artreportofbridgehealthmonitoring

Abstract

Thedamagediagnosisandhealthmonitoringofbridgestructuresareactiveareasofresearchinrecentyears.Comparingwiththeaerospaceengineeringandmechanicalengineering,civilengineeringhasthespecialitiesofitsowninpractice.Forexample,becausebridges,aswellasmostcivilengineeringstructures,arelargeinsize,andhavequitelownaturalfrequenciesandvibrationlevels,atlowamplitudes,thedynamicresponsesofbridgestructurearesubstantiallyaffectedbythenonstructuralcomponents,unforeseenenvironmentalconditions,andchangesinthesecomponentscaneasilytobeconfusedwithstructuraldamage.Allthesegivethedamageassessmentofcomplexstructuressuchasbridgesastillchallengingtaskforbridgeengineers.Thispaperfirstlypresentsthedefinitionofstructuralhealthmonitoringsystemanditscomponents.Then,thefocusofthediscussionisplacedonthefollowingsections:

①thelaboratoryandfieldtestingresearchonthedamageassessment;②analyticaldevelopmentsofdamagedetectionmethods,including（a）signatureanalysisandpatternrecognitionapproaches,（b）modelupdatingandsystemidentificationapproaches,（c）neuralnetworksapproaches;and③sensorsandtheiroptimumplacements.Thepredominanceandshortcomingsofeachmethodarecomparedandanalyzed.Recentexamplesofimplementationofstructuralhealthmonitoringanddamageidentificationaresummarizedinthispaper.Thekeyproblemofbridgehealthmonitoringisdamageautomaticdetectionanddiagnosis,anditisthemostdifficultproblem.Lastly,researchanddevelopmentneedsareaddressed.

1Introduction

Duetoawidevarietyofunforeseenconditionsandcircumstance,itwillneverbepossibleorpracticaltodesignandbuildastructurethathasazeropercentprobabilityoffailure.Structuralaging,environmentalconditions,andreuseareexamplesofcircumstancesthatcouldaffectthereliabilityandthelifeofastructure.Thereareneedsofperiodicinspectionstodetectdeteriorationresultingfromnormaloperationandenvironmentalattackorinspectionsfollowingextremeevents,suchasstrong-motionearthquakesorhurricanes.Toquantifythesesystemperformancemeasuresrequiressomemeanstomonitorandevaluatetheintegrityofcivilstructureswhileinservice.SincetheAlohaBoeing737accidentthatoccurredonApril28,1988,suchinteresthasfosteredresearchintheareasofstructuralhealthmonitoringandnon-destructivedamagedetectioninrecentyears.

AccordingtoHousner,etal.（1997）,structuralhealthmonitoringisdefinedas“theuseofin-situ,non-destructivesensingandanalysisofstructuralcharacteristics,includingthestructuralresponse,fordetectingchangesthatmayindicatedamageordegradation”[1].Thisdefinitionalsoidentifiestheweakness.WhileresearchershaveattemptedtheintegrationofNDEwithhealthmonitoring,thefocushasbeenondatacollection,notevaluation.Whatisneededisanefficientmethodtocollectdatafromastructurein-serviceandprocessthedatatoevaluatekeyperformancemeasures,suchasserviceability,reliability,anddurability.So,thedefinitionbyHousner,etal.（1997）shouldbemodifiedandthestructuralhealthmonitoringmaybedefinedas“theuseofin-situ,nondestructivesensingandanalysisofstructuralcharacteristics,includingthestructuralresponse,forthepurposeofidentifyingifdamagehasoccurred,determiningthelocationofdamage,estimatingtheseverityofdamageandevaluatingtheconsequencesofdamageonthestructures”（Fig.1）.Ingeneral,astructuralhealthmonitoringsystemhasthepotentialtoprovidebothdamagedetectionandconditionassessmentofastructure.

Assessingthestructuralconditionwithoutremovingtheindividualstructuralcomponentsisknownasnondestructiveevaluation（NDE）ornondestructiveinspection.NDEtechniquesincludethoseinvolvingacoustics,dyepenetrating,eddycurrent,emissionspectroscopy,fiber-opticsensors,fiber-scope,hardnesstesting,isotope,leaktesting,optics,magneticparticles,magneticperturbation,X-ray,noisemeasurements,patternrecognition,pulse-echo,ra-diography,andvisualinspection,etc.Mostofthesetechniqueshavebeenusedsuccessfullytodetectlocationofcertain

elements,cracksorwelddefects,corrosion/erosion,andsoon.TheFederalHighwayAdministration（FHWA,USA）wassponsoringalargeprogramofresearchanddevelopmentinnewtechnologiesforthenondestructiveevaluationofhighwaybridges.Oneofthetwomainobjectivesoftheprogramistodevelopnewtoolsandtechniquestosolvespecificproblems.Theotheristodeveloptechnologiesforthequantitativeassessmentoftheconditionofbridgesinsupportofbridgemanagementandtoinvestigatehowbesttoincorporatequantitativeconditioninformationintobridgemanagementsystems.Theyhopedtodeveloptechnologiestoquickly,efficiently,andquantitativelymeasureglobalbridgeparameters,suchasflexibilityandload-carryingcapacity.Obviously,acombinationofseveralNDEtechniquesmaybeusedtohelpassesstheconditionofthesystem.Theyareveryimportanttoobtainthedata-baseforthebridgeevaluation.ButitisbeyondthescopeofthisreviewreporttogetintodetailsoflocalNDE.

Healthmonitoringtechniquesmaybeclassifiedasglobalandlocal.GlobalattemptstosimultaneouslyassesstheconditionofthewholestructurewhereaslocalmethodsfocusNDEtoolsonspecificstructuralcomponents.Clearly,twoapproachesarecomplementarytoeachother.Allsuchavailableinformationmaybecombinedandanalyzedbyexpertstoassessthedamageorsafetystateofthestructure.

Structuralhealthmonitoringresearchcanbecategorizedintothefollowingfourlevels:

（I）detectingtheexistenceofdamage,（II）findingthelocationofdamage,（III）estimatingtheextentofdamage,and（IV）predictingtheremainingfatiguelife.TheperformanceoftasksofLevel（III）requiresrefinedstructuralmodelsandanalyses,localphysicalexamination,and/ortraditionalNDEtechniques.ToperformtasksofLevel（IV）requiresmaterialconstitutiveinformationonalocallevel,materialsagingstudies,damagemechanics,andhigh-performancecomputing.Withimprovedinstrumentationandunderstandingofdynamicsofcomplexstructures,healthmonitoringanddamageassessmentofcivilengineeringstructureshasbecomemorepracticalinsystematicinspectionandevaluationofthesestructuresduringthepasttwodecades.

Moststructuralhealthmonitoringmethodsundercurrentinvestigationfocusonusingdynamicresponsestodetectandlocatedamagebecausetheyareglobalmethodsthatcanproviderapidinspectionoflargestructuralsystems.Thesedynamics-basedmethodscanbedividedintofourgroups:

①spatial-domainmethods,②modal-domainmethods,③time-domainmethods,and④frequency-domainmethods.Spatial-domainmethodsusechangesofmass,damping,andstiffnessmatricestodetectandlocatedamage.Modal-domainmethodsusechangesofnaturalfrequencies,modaldampingratios,andmodeshapestodetectdamage.Inthefrequencydomainmethod,modalquantitiessuchasnaturalfrequencies,dampingratio,andmodelshapesareidentified.Thereversedynamicsystemofspectralanalysisandthegeneralizedfrequencyresponsefunctionestimatedfromthenonlinearauto-regressivemovingaverage（NARMA）modelwereappliedinnonlinearsystemidentification.Intimedomainmethod,systemparametersweredeterminedfromtheobservationaldatasampledintime.Itisnecessarytoidentifythetimevariationofsystemdynamiccharacteristicsfromtimedomainapproachifthepropertiesofstructuralsystemchangewithtimeundertheexternalloadingcondition.Moreover,onecanusemodel-independentmethodsormodel-referencedmethodstoperformdamagedetectionusingdynamicresponsespresentedinanyofthefourdomains.Literatureshowsthatmodelindependentmethodscandetecttheexistenceofdamagewithoutmuchcomputationalefforts,buttheyarenotaccurateinlocatingdamage.Ontheotherhand,model-referencedmethodsaregenerallymoreaccurateinlocatingdamageandrequirefewersensorsthanmodel-independenttechniques,buttheyrequireappropriatestructuralmodelsandsignificantcomputationalefforts.Althoughtime-domainmethodsuseoriginaltime-domaindatameasuredusingconventionalvibrationmeasurementequipment,theyrequirecertainstructuralinformationandmassivecomputationandarecasesensitive.Furthermore,frequency-andmodal-domainmethodsusetransformeddata,whichcontainerrorsandnoiseduetotransformation.Moreover,themodelingandupdatingofmassandstiffnessmatricesinspatial-domainmethodsareproblematicanddifficulttobeaccurate.Therearestrongdevelopment

trendsthattwoorthreemethodsarecombinedtogethertodetectandassessstructuraldamages.Forexample,severalresearcherscombineddataofstaticandmodalteststoassessdamages.Thecombinationcouldremovetheweaknessofeachmethodandcheckeachother.Itsuitsthecomplexityofdamagedetection.

Structuralhealthmonitoringisalsoanactiveareaofresearchinaerospaceengineering,buttherearesignificantdifferencesamongtheaerospaceengineering,mechanicalengineering,andcivilengineeringinpractice.Forexample,becausebridges,aswellasmostcivilengineeringstructures,arelargeinsize,andhavequitelownaturalfrequenciesandvibrationlevels,atlowamplitudes,thedynamicresponsesofbridgestructurearesubstantiallyaffectedbythenon-structuralcomponents,andchangesinthesecomponentscaneasilytobeconfusedwithstructuraldamage.Moreover,thelevelofmodelinguncertaintiesinreinforcedconcretebridgescanbemuchgreaterthanthesinglebeamoraspacetruss.Allthesegivethedamageassessment