Forensic Diagnosis on the Overall Collapse of a Composite Box-Girder Bridge

Abstract

On 24 August 2012, a box-girder bridge collapsed under overload in China. The failed bridge served as the ramp of a city viaduct. The accident occurred when four trucks were crossing the bridge. It caused three deaths, five injuries and traffic disruption. This paper presents a forensic diagnosis of the failed bridge. Four possible causes of the structural failure are analyzed and verified through on-site graphic investigation, structural analysis and numerical simulation. Based on the accumulated information, the failure mechanism is derived and the failure process is identified. The results indicate that overall instability under the unusually heavy weight of vehicles led to rotation of the girder but did not directly cause the failure of the superstructure. A large redistribution of vertical reactions due to geometrical nonlinearity led to failure of the bent caps, which was the primary reason for the collapse of the bridge. It is suggested that lateral safety should be taken seriously for similar types of bridges and substructure strength should be adequate for future design of similar structures, especially in heavy vehicle areas.