4. Practical Analysis of Bridges on Isolation Bearings with Bi‐Linear Hysteresis Characteristics

Abstract

Various equivalent elastic models specified in current bridge engineering practices for the seismic analysis of base‐isolated bridges are summarized and evaluated. Two additional methods proposed by the California Department of Transportation (CALTRANS) are validated based on their predictions of the maximum inelastic seismic responses of base‐isolated bridges. The CALTRANS proposed methods are implemented with an empirical model for the determinations of the effective stiffness and equivalent viscous damping ratios of isolation units and base‐isolated bridges. A modal strain energy method combined with the concept of component energy ratio is utilized to formulate the “composite damping ratio” of an entire base‐isolated bridge. A five‐span regular bridge subjected to four design earthquakes and ten recorded ground motions is employed to investigate the accuracy of prediction using various equivalent elastic methods.