Fragility analysis of tall pier bridges subjected to near-fault pulse-like ground motions

摘要

More than 40% of bridges in Southwest China have piers over 40 m height. The seismic behaviour of these bridges is critical, especially exposed to near-fault pulse-like ground motions. This paper conducts fragility analyses to assess the seismic vulnerability of tall pier bridges under near-fault motions. Fragility curves are developed for a typical 50-m tall pier and a 10 m conventional pier with probabilistic seismic demand models (PSDMs). When developing the PSDMs, curvature ductility at pier base is used as the demand parameter; the 5% damped spectral acceleration of the fundamental period (S-a(T-1, 5%)) is employed as an intensity measure of the motions. Results show that the 50 m pier is less vulnerable than the 10 m pier under both the near-fault and far-field motions and is unlikely to collapse in real earthquake events. Furthermore, the seismic fragility of the 50 m pier is found highly related to the pre-defined damage state capacities, indicating that the damage states should be carefully specified to properly estimate the vulnerability of tall piers. Finally, analyses are conducted for piers with heights of 40, 60, 70, and 80 m, extending the conclusions obtained from 50 m pier to a class of tall piers.