Probabilistic Damage Analysis of Isolated Steel Tub Girder Bridge Excited by Near and Far Fault Ground Motions

Friction Pendulum Bearing (FPB) has emerged as a popular solution for damage protection of bridges under seismic events. The study presents the probabilistic damage analysis for the isolated tub girder continuous bridge under the near and the far fault earthquakes using fragility analysis. The steel tub girder continuous bridge is considered with friction pendulum isolator as the seismic isolation mechanism. In order to represent the hysteretic behavior of friction pendulum isolators, a bilinear force-deformation model was used. Fragility curves are developed for  various damage measures namely rotational ductility of pier and girder displacement with the peak ground acceleration (PGA) as  an intensity measure (IM). Incremental dynamic analyses (IDA) were performed to develop the fragility curves and probabilistic damage model considering the four threshold damage states. The results suggest that in the case of low PGA level, the near fault earthquake leads to the high probability of exceedance in the case of isolated tub girder bridge. Damage model for piers and girder were developed to correlate component responses levels to overall bridge deterioration states. Finally, recommendations for the bridge developers in the stage of the early bridge seismic isolation design utilizing friction pendulum isolators are discussed.