Seismic scenario reproduction and damage mechanism analysis of Liuhuanggou Bridge under near-fault earthquake

Near-fault earthquakes can cause more intricate dynamic responses and potentially lead to severe damage to bridge structures compared to far-field earthquakes. In January 8, 2022, a 6.9-magnitude earthquake struck Menyuan, Qinghai Province, resulting in the disruption of the Lanzhou-Urumqi high-speed railway. The Liuhuanggou Bridge is the first high-speed railway bridge in the world to have undergone severe earthquake damage. In order to investigate the reasons for the seismic damage and girder falling mechanism, this study established a comprehensive nonlinear analysis model that considers the entire process from mild damage to complete failure of bridge components. Based on the LS-DYNA explicit dynamic analysis software, the model accurately simulates the collision, girder falling, and bearing damage. Based on limited field investigation data and combined with theoretical methods, reasonable seismic inputs are constructed, which accurately reproduce the bridge damage. The analysis results indicate that the girders and piers of high-speed railway simply supported bridges exhibit good seismic performance under seismic, while the bearings and shear keys are damaged. The seismic intensity (IX degree) significantly exceeded the fortification intensity (VII degree) of the bridge. The near-fault earthquake velocity pulse, inappropriate seismic measures, and nonuniform excitation of cross-fault earthquake are significant factors leading to the collapse of the Liuhuanggou Bridge. Further research is needed for the rational selection of bridge types in fault zones. The numerical results and conclusions of this study can provide a reference for the seismic design of high-speed railway simply supported bridges built near faults.