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 performance of various components of such bridge systems. This study proposes a two-step system identification method for identifying structural parameters from strong motion records. The first step entails identification of complex modal parameters of a nonclassically damped base-isolated bridge-pier-pile-foundation system for which necessary theoretical formulations are first derived. In the second step a global search scheme is introduced to identify the structural parameters of the system corresponding to the identified modal parameters. The proposed system identification method is applied to two base-isolated bridges such that recorded responses at pier cap and girder are successfully recreated for one main shock and four aftershocks of the 1995 Kobe earthquake and modal and structural parameters are identified. performance of the base-isolation system is evaluated by comparing the physical properties of the bearings, determined from experimental data, with the identified values and is found to be satisfactory in both bridges.