System Identification of Structures from Seismic Response Data via Wavelet Packet Method

This paper presents a procedure of establishing the discrete equations of motion for a structure via wavelet packet method from its measured responses and inputs. Then, the natural frequencies, damping ratios and mode shapes of the structure can be directly determined. The proposed procedure is applied to process the acceleration responses of a five-story steel frame, subjected to 8%, 20%, 40%, 52% and 60% of the strength of the Kobe earthquake, in shaking table tests. The steel frame responded nonlinearly when it subjected to 60% Kobe earthquake, while it responded linearly when it subjected to the other strengths of the Kobe earthquake. This work also investigates the differences in modal parameters identified from the responses to the inputs with different strengths of the Kobe earthquake. The accuracy of the present results is confirmed by comparing the present results with the published obtained from the responses to the 8% Kobe earthquake input.