Effect of Seismic Ground Motions at Near-Fault Canyon Sites on the Seismic Fragility and Resilience of High-Pier Rigid-Frame Bridges

This study investigated the effect of near-fault spatially varying ground motions on the seismic fragility and resilience of a long-span high-pier highway bridge crossing a canyon with a water layer. All the ground motions in the fragility analysis were obtained based on the stochastic finite-fault method combined with the indirect boundary-element method to account for both the near-fault and local site effects. This approach is advantageous because it includes the influence of the near-fault, irregular topography, soil saturation characteristics, and water layer, which affect the fragility, functionality, and resilience of the bridge. Moreover, the study compared the components and system fragilities of the bridge under uniform and nonuniform near-fault ground motions and discusses the bridge functionality and resilience under three earthquake scenarios, considering the bridge location at the hanging wall and footwall with the same fault distances. The results indicated that the damage probabilities of the bridge components and system under nonuniform near-fault ground motions are higher than those under uniform excitations. The difference in the collapse damage probabilities of the bridge system can reach 24% when the peak ground velocity is 0.5 m/s. This suggests that the bridge resilience is significantly overestimated when uniform near-fault ground motions are adopted, and a decrease of 0.49 in resilience occurs under the assumed 2008 Mw 6.3 Damxung Earthquake after 200 days when considering the local site effect. The water layer slightly increases the bridge fragility, whereas it significantly decreases the bridge resilience, which is ascribed to the longer time required for underwater recovery.