Extended Blind Modal Identification Technique for Nonstationary Excitations and Its Verification and Validation

Abstract

Recently the authors developed an output-only (or blind) identification technique for the modal identification of structures under ambient/free vibrations. In the present study, this method is extended to incorporate nonstationary unknown inputs—a feature that existing output-only methods are unable to replicate. The method employs a so-called PARAllel FACtor technique to decompose the third-order tensor that is built using the spatial time–frequency matrices of the response signals in order to find the mode shapes and modal coordinates’ auto time–frequency distribution (TFD). The proposed method is first verified using a synthetic data set and then used to extract the modal parameters from vibration data recorded during shaking table tests on the International Institute of Earthquake Engineering and Seismology (IIEES) test structure. The accuracy of the blind identification results is assessed through comparisons with a well-established input–output identification method, namely, a well-known combination of the eigensystem realization algorithm and the observer/Kalman filter identification (ERA/OKID) method. Next, rigidities of the connections of the IIEES Test Structure are identified through a finite-element (FE) model updating procedure. Finally, the proposed method is validated through comparisons between responses predicted using the updated FE model and those directly recorded in additional shaking table tests that were not used in model updating studies.