Onebranchofstructuralhealthmonitoring(SHM)utilizesdynamicresponsemeasurementstoassessthestructuralintegrityofcivilinfrastructures.Inparticular,modalfrequencyisawidelyadoptedindicatorforstructuraldamagesinceitssquareisproportionaltostructuralstiffness.However,ithasbeendemonstratedinvariousSHMprojectsthatthisindicatorissubstantiallyaffectedbyfluctuatingenvironmentalconditions.Inordertoprovidereliableandconsistentinformationonthehealthstatusofthemonitoredstructures,itisnecessarytodevelopamethodtofilterthisinterference.Thisstudyattemptstomodelandquantifytheenvironmentalinfluenceonthemodalfrequenciesofreinforcedconcretebuildings.Dailystructuralresponsemeasurementsofatwenty-twostoryreinforcedconcretebuildingwerecollectedandanalyzedoveraone-yearperiod.TheBayesianspectraldensityapproachwasutilizedtoidentifythemodalfrequenciesofthisbuildinganditwasclearlyseenthatthetemperatureandhumidityfluctuationinducednotablevariations.Amathematicalmodelwasdevelopedtoquantifytheenvironmentaleffectsandmodelcomplexitywastakenintoconsideration.BasedonaTimoshenkobeammodel,thefullmodelclasswasconstructedandotherreduced-ordermodelclasscandidateswereobtained.Then,theBayesianmodalclassselectionapproachwasemployedtoselecttheonewiththemostsuitablecomplexity.Theproposedmodelsuccessfullycharacterizestheenvironmentalinfluenceonthemodalfrequencies.Furthermore,theestimateduncertaintyofthemodelparametersallowsforassessmentofthereliabilityoftheprediction.Thisstudynotonlyimprovestheunderstandingaboutthemonitoredstructure,butalsoestablishesasystematicapproachforreliablehealthassessmentofreinforcedconcretebuildings.
