Modal Identification of an Arch Dam during Various Earthquakes

Accurate prediction of the dynamic response of an arch dam during an earthquake is a difficult challenge due to complexity of dam-foundation-reservoir interaction andlimitations of analysis methods. System identification is a reliable method for assessment of real behavior of structures during an event. Results of system identification analysiscan be regarded for improvement of numerical models. Accurate evaluation of dynamic parameters of an arch dam demands numerous recorded data. Hence, in this research,Pacoima Dam is selected as a case study due to its extreme instrumentation and diversityof recorded events and investigations. Identification of dynamic parameters of the dam is conducted by ARX method considering non-uniform ground motions, applying recordeddata of 3 different earthquakes. Time variation of modal parameters of the dam isdetermined by time windowing of the earthquake records. The results are compared to the results of previous system identification investigations and forced vibration tests.Results of modal frequencies, time variations of modal parameters during the studied earthquakes and the reasons of some discrepancies with the results of previousinvestigations are discussed. The results indicate that considering non-uniform excitation is essential to increase the accuracy of modal parameters estimation. The behavior of thedam is different under slight and large motions which main reasons can be non-linearbehavior of material or deformation of foundation. Unconformity of the identification results from forced vibration tests and earthquake records might be due to these reasons.It seems that considering seismic or ambient vibration records besides forced vibration tests is essential for accurate evaluation of dynamic properties. Also, investigation of timevariations of modal properties is necessary for reliable assessment of seismic behavior ofan arch dam.

کلیدواژه ها:

System Identification ، MISO ARX ، Time Variant Modal Properties ، Arch Dam ، Non-Uniform Ground Motion