Seismic Damage Inversion of Multi-Span Simply Supported Bridge Under Near-Field Strong Earthquakes: A Case Study of the Yematan Bridge

Near-fault impulse earthquakes induce complex dynamic responses in bridge structures, potentially resulting in significant structural damage. On May 22, 2021, a magnitude 7.4 earthquake struck MaDuo County in the Guoluo Autonomous Prefecture of Qinghai Province, with the Yematan Bridge sustaining the most extensive damage during this seismic event. This study employs synthetic near-fault impulsive ground motions and the LS-DYNA explicit dynamic analysis software to investigate the mechanisms underlying the observed seismic damage and the subsequent failure of girders. The simulations effectively replicated the collisions involving the main girder, the damage to the shear keys, and the falling girders. Furthermore, post-earthquake soil exploration data, analyzed using DEEPSOIL site analysis software, are integrated to assess the amplification effects of ground vibrations at the bridge site. The analysis revealed that the longitudinal peak ground acceleration (PGA) experienced by the Yematan Bridge is approximately 6.8[Formula: see text]m/[Formula: see text], while the transverse PGA is about 4.2[Formula: see text]m/[Formula: see text]. The damage to the bridge occurred in two distinct stages: initially involving collisions between the shear keys and the main girder, followed by a “domino effect”, leading to the failure of multiple girders. The primary factors contributing to the structural damage included impulsive seismic forces, short pier heights, transient bearing failures, and substantial longitudinal and transverse displacements of the main girder due to ground vibrations and inertial effects, which ultimately resulted in shear key damage and the subsequent collapse of girders. Despite the Yematan Bridge being designed to withstand seismic intensity rated at VIII, DEEPSOIL’s inversion analysis indicated a bedrock PGA of 4.26[Formula: see text]m/[Formula: see text] and a corresponding seismic intensity of IX. At the same time, the earthquake-resistant rating for MaDuo County is designated as VIII. This discrepancy in seismic intensity zones significantly exacerbated the severity of the girder failures. The numerical findings and conclusions presented in this study provide critical insights for the seismic design of simply supported highway bridges located in near-fault regions.