Current caltrans analysis methods of bridges isolated with bi-linear hysteresis bearings

ABSTRACT

Two methods were recently proposed by the California Department of Transportation (CALTRANS) for the analysis of bridges isolated with bearings whose hysteresis behavior can be appropriately represented by a bi-linear model. In the first CALTRANS proposed method, the hysteresis behavior of a base-isolated regular bridge was idealized by a bi-linear model in the direction of consideration. Based on the hysteresis loop of the entire base-isolated bridge, an empirical model was used to determine the effective period and equivalent viscous damping ratio of the bridge. In the second CALTRANS proposed method, the empirical model was employed to determine the effective stiffness and equivalent damping ratio of isolation bearings rather than the base-isolated bridge. A five-span regular bridge subjected to three design earthquakes and ten recorded ground motions is employed to investigate the accuracy of prediction using CALTRANS proposed methods. The analysis results are compared with those from the analyses using AASHTO isolation guide specifications, JPWRI menshin design manual and the inelastic analysis program DRAIN-2D.(AU)