System identification of two base-isolated bridges using seismic records

Identification of system parameters from seismic accelerations recorded on a base-isolated bridge provides an excellent opportunity to examine the per formance of various components of such bridge systems. This study proposes a two-step system identification method for identifying structural paramete rs from strong motion records. The first step entails identification of com plex modal parameters of a nonclassically damped base-isolated bridge-pier- pile-foundation system for which necessary theoretical formulations are fir st derived. In the second step a global search scheme is introduced to iden tify the structural parameters of the system corresponding to the identifie d modal parameters. The proposed system identification method is applied to two base-isolated bridges such that recorded responses at pier cap and gir der are successfully recreated for one main shock and four aftershocks of t he 1995 Kobe earthquake and modal and structural parameters are identified. performance of the base-isolation system is evaluated by comparing the phy sical properties of the bearings, determined from experimental data, with t he identified values and is found to be satisfactory in both bridges.