Collapse of the Baihua Bridge under Near-Fault Ground Motion: Finite-Element Analysis with Multiscale Model

Abstract

Investigating the seismic behavior and safety of structures subjected to near-fault ground motions is vital. Cases involving damages to or failure of structures during earthquakes provide valuable opportunities to achieve the aforementioned goal, as these are the actual results of in situ tests of full-scale structures. The Baihua Bridge, a concrete continuous-curved girder bridge, was located at the epicenter area of the 2008 Wenchuan earthquake in China, and it collapsed partially in the quake. This study focuses on exploring the collapse mechanism of curved multispan continuous bridges subjected to near-fault strong ground motions. A refined multiscale finite-element model was used for analysis of the seismic response and simulation of the collapse process of the bridge, and the seismograms recorded by the local observation station during the Wenchuan earthquake were employed. The results show multiple cases of failure mechanism-induced serious damage to the main bearing components of the bridge structure, resulting in the progressive collapse of a unit consisting of curved girders. The redistribution of the internal forces after unseating, swinging of the girders, and collisions between the falling girders and piers were the main reasons for the progressive collapse of the bridge. The collapse could have been avoided by increasing the seating length of the girders or their resistance to negative bending moments. Configuring the stirrups according to the new code could improve the shear capacities of most piers by 62%–89%, which would meet the shear demands. However, configuring the longitudinal reinforcements according to the new code could increase the flexural capacities by 37%–39%, which would remain insufficient for ensuring the safety of the piers. The longitudinal reinforcement ratio of high pier columns should be individually designed, especially in curved segments or on piers with fixed bearings.