Dynamic response and fragility of mountain bridges under the coupled effects of transverse earthquakes and landslides

Abstract

Earthquake-induced debris flow landslides pose a serious threat to bridge structures. However, current research on the dynamic response and damage mechanisms of bridges due to debris flow landslides is still insufficient; the fragility analysis of bridges under the combined effects of earthquakes and related geological hazards needs further improvement. In this paper, a bridge dynamic response simulation method is proposed for the coupled effects of transverse earthquakes and debris flow landslides. The method first establishes an integrated model of the mountain and bridge piers, using the discrete element method to calculate the dynamic impact of the landslide on the piers. Subsequently, a nonlinear dynamic model of the bridge is established using the finite element method. By inputting the time histories of transverse seismic motion and landslide impact, the coupled effects of transverse earthquakes and landslides are analyzed. The paper analyzes the influence of sliding distance, landslide length, and slope gradient on the dynamic response and fragility of bridges through case studies. Research reveals that the shear capacity of the pier under the coupled effects of earthquakes and landslides should be considered. The combined effects also increase the displacement response of the piers, with the maximum pier top drift ratio of the case bridge increasing by 334 % at a 35° slope compared to the earthquake-only condition. Under the coupled effects of earthquakes and landslides, the piers will experience significant residual deformation in the direction of the landslide. Increases in sliding distance, landslide length, and slope gradient all increase the fragility of bridges under various damage states, with the complete damage probability of the case bridge rising from 5 % under earthquake-only conditions to 47 % at a 35° slope. The slope gradient has the greatest sensitivity to the fragility of bridges, followed by the sliding distance, and finally the landslide length.