Influence of Pier Stiffness Degradation on Soil-Structure Interaction in Base-Isolated Bridges

Abstract

Identification of system parameters by recorded accelerographs on base-isolated bridges during earthquakes provides an opportunity to investigate the performance of such bridges. Stiffness degradation in reinforced concrete piers of four multispan continuous base-isolated bridges in Japan during eighteen earthquakes is examined by using system identification results and theoretical load-displacement curves of reinforced concrete piers. Soil-structure interaction (SSI) effect identified in these bridges is found to be independent of free field acceleration and weakly dependent on dynamic soil properties. This apparent contradiction with the popular belief of strong SSI in weaker soil prompted to consider the fact that with increasing seismic intensity, similar degradation in pier stiffness also takes place and it is the ratio of pier and foundation stiffness