Random vibration and seismic fragility analysis of continuous girder bridges under near-fault ground motions

The construction sites of bridges are sometimes located near active seismic faults. Thus, there is an urgent need to develop a unified and accurate method for nonlinear stochastic dynamic responses and seismic fragility analyses to evaluate the seismic safety levels of continuous girder bridge structures under near-fault ground motions and to improve their seismic performance. Considering the near-fault ground motions as a kind of typical stochastic process excitation, this paper proposes a new accurate and versatile framework based on the direct probability integral method (DPIM) for analyzing nonlinear random vibration responses and seismic fragilities of continuous girder bridges. Here, the DPIM is developed to accurately and efficiently calculate the random vibration responses of a nonlinear continuous girder bridge. Then, by considering several damage states of the girder bridge system and referring to the first-passage failure criterion of dynamic reliability, the seismic fragilities of nonlinear continuous girder bridges are analyzed via DPIM. Finally, the numerical results of a four-span nonlinear continuous girder bridge under near-fault stochastic ground motions are displayed, thus verifying the accuracy of DPIM. In addition, the effects of near-fault pulse-like and nonpulse ground motions on the seismic fragility curves of the nonlinear continuous girder bridge are compared. The results indicate that the velocity pulses of near-fault ground motions cause more damage to the continuous girder bridge structures, thus increasing the exceedance probability of bridge structures entering different damage states. © 2024 Editorial Board of Journal of Harbin Engineering. All rights reserved.