Assessment of Vibration-based Damage Identificatio

 StructuralHealthMonitoring: DOI:10.1177/147592170934096420098:443originallypublishedonline6August2009StructuralHealthMonitoringA.PhilipsAdewuyi,ZhishenWuandN.H.M.KammrujamanSerkerStrainMeasurementsAssessmentofVibration-basedDamageIdentificationMethodsUsingDisplacementandDistributed  Publishedby:    : : : : : byQiboMaoonSeptember22,2010shm.sagepub.comDownloadedfrom443AssessmentofVibration-basedDamageIdentificationMethodsUsingDisplacementandDistributedStrainMeasurementsA.PhilipsAdewuyi,ZhishenWu*andN.H.M.KammrujamanSerkerDepartmentofUrbanandCivilEngineering,IbarakiUniversity4-12-1Nakanarusawa-cho,Hitachi,Ibaraki316-8511,JapanAccuratemeasurementandmonitoringofvibrationcharacteristicsiscriticalforproperdetectionofthelocationandseverityofdamage.However,experimentallymeasuredmodalpropertiesareinevitablycorruptedbymeasurementnoiseanderrors,whichcouldrendermostvibration-basedstructuraldamageidentificationalgorithmsunreliableforcivilstructuralhealthmonitoring(SHM).Thisarticle,throughcomputersimulationandexperimentalinvestigationofasimplysupportedbeam,comparativelyevaluatestheperformanceofthesetechniquesforpracticalcivilSHMbyusingdisplacementmodesfromaccelerometersandlong-gagedistributedstrainmeasurements.Mostofallthetechniquesprovedunreliablefordamageidentificationusingnoisymeasurementsfromaccelerometers,whilesuccessfulwithdistributedstrainmeasurements.Thefindingsrevealthatlong-gagedistributedstrainmeasurementsaremuchmoreefficientchoiceoverthetraditionalmeasurementtechniquesforreliablecivilSHM.Itmaythereforebeconcludedthattheperformanceofsomealgorithmsmightbeimprovedforapplicationtocivilinfrastructurebyusingdistributedstrainfiberopticsensingmeasurementtechniques.KeywordsdamageidentificationdistributedstrainFBGsensorsmeasurementnoisestructuralhealthmonitoring1IntroductionConditionmonitoringofcivilinfrastructurehasbecomeafundamentalissueforstructuralsafetyandintegrity.Damagehasbeendefinedinamorepracticalsenseaschangesintroducedintoasystemthatadverselyaffectitscurrentorfutureperformance[1].Changesinstructuraldynamicparametershavebeenextensivelyutilizedasaneffectivetoolforstructuralintegrityassess-mentanddamageidentificationattheearliestpossiblestage.Theextensionofvibration-baseddamageidentification(VBDI)techniquestocivilinfrastructureisincreasinglyreceivingattentionbecauseoftheincreaseinsocioeconomicandenvironmentaldemandsforperiodicassessmentofstructuralperformanceandtheirsafetyagainstlong-termdeterioration.ThebasicconceptofVBDIisthatanydegradationofthestructuralpropertiesresultsinchangesofthemodalparametersnamely,naturalfrequencies,modeshapes,andmodal*Authortowhomcorrespondenceshouldbeaddressed.E-mail:[e-mail]2–18appearincoloronline:TheAuthor(s),2009.Reprintsandpermissions:(6):0443–19[1475-9217(200911)8:6;443–1910.1177/1475921709340964]byQiboMaoonSeptember22,2010shm.sagepub.comDownloadedfromdampingratios.Perturbationsinglobalstructuraldynamiccharacteristicsareanalyzedasindicatorsofthepresence,location,andseverityofdamagebycomparingfeaturesextractedfromdynamicresponseparametersbeforeandafterdamagewithorwithoutstructuralmodelinformation.Severaldamageidentificationtechniqueshavebeendevelopedandsuccessfullyinvestigatedbasedontheresonantfrequencies,modeshapeanditsderivatives,modalflexibilityanditsderivatives,modalstiffness,modalstrainenergy,frequencyresponsefunction(FRF),anditscur-vatureandpowerspectraldensity.Therefore,physicalquantitiesmostrelevantandsensitivetothestructuralpropertiesofinterestareutilizedformonitoringpurposes.ExtensiveliteraturereviewsandadvancesinVBDIhavebeenreportedbySohnetal.[1],Doeblingetal.[2],andCardenandFanning[3].However,somechallengesstillconfrontthepracticalityofVBDItechniques.First,accuratemeasurementsandclosemonitoringofvibrationcharacteristicsaretherequisitesforearlydetec-tionofdamageandreliableconditionassessmentinstructures.Forexample,naturalfrequencies,thougheasytomeasurewithhighaccuracy,seemtoo‘global’todetectlocaldamage.Itisnote-worthythatregardlessofthetypeofmeasure-menttechniquesusedforstructuralidentification,measurementsareinevitablypollutedbynoiseduetoexperimentalandextractiontechniques,andenvironmentalfactors.Also,whereasspatialspecificityandhighsensitivitytodamagearethemajoradvantagesofvibrationmodeshapesandtheirderivatives,theirsusceptibilitytonoiseisofgreatconcern[4].Inaddition,theadaptationofVBDImethodstocivilengineeringinfrastructurehasbeencomplicatedbytherelativelylargesizeandinherentcomplexityofthesestructures,thediver