Modal identification of structures from ambient vibration, free vibration,and seismic response data via subspace approach

This work presents a unified procedure for determining the natural frequenc ies, modal damping ratios and modal shapes of a structure from its ambient vibration, free vibration and earthquake response data. To evaluate the coe fficient matrices of a state-space model, the proposed procedure applies a subspace approach cooperating with an instrumental variable concept. The dy namic characteristics of a structure are determined from the coefficient ma trices. The feasibility of the procedure is demonstrated through processing an in situ ambient vibration measurement of a five-storey steel frame, an impulse response measurement of a three-span continuous bridge, and simulat ed earthquake responses of five-storey steel frames from shaking table test s. The excellent agreement of the results obtained herein with those publis hed previously confirms the feasibility of the present procedure. Copyright (C) 2001 John Wiley & Sons, Ltd.