Abstract:With an actual skewed continuous rigid-frame highway bridge in the western US chosen as the research object, this paper investigated the impact of differences in the vulnerability of unequal height piers and the skew angle on the seismic fragility of piers. The model sample database was generated using 100 ground motions inputted in the longitudinal direction of the bridge considering the uncertainties of structural parameters and ground motion. Then, with peak ground acceleration taken as the intensity measure, the seismic responses of each pier were obtained via nonlinear time history analysis using OpenSees. The curvature ductility ratio of piers was defined to measure the damage state of the bridge. After the pier damage indexes were derived, seismic fragility curves of piers were obtained with reliability theory, and the damage modes and characteristics of piers were judged. On this basis, fragility analysis was performed by changing the skew angle, and the impact of this change on the seismic fragility of piers was obtained. This study found that the damage probability of the shortest pier was greater than that of the other piers, and the top and the bottom of piers first entered the plastic stage. The seismic responses of bridge were influenced significantly by skew angle, and the damage sequence of each pier was related to the characteristics of the bridge structure. The fragility of two-side pier columns at the same bent pier was opposite the variation trend of the skew angle; serious damage corresponded to an obvious trend. The skewed rigid-frame bridge with unequal height was weak in the shortest pier. Moreover, as the skew angle increases, the damage of the short pier at an obtuse angle should be given more attention and enhanced design criteria should be developed, especially for the seismic design of skewed rigid-frame bridges.
