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 6.8m/s(2), while the transverse PGA is about 4.2m/s(2). 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 4.26m/s(2) 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.

A series of numerical simulations were completed to investigate the behavior of intact, fire -damaged, and Carbon Fiber -Reinforced Polymers (CFRP) retrofitted reinforced concrete (RC) bridge columns of varying sizes subjected to vehicle collisions. Three-dimensional finite element models of isolated RC columns and their foundation systems surrounded by soil volumes were developed using LS-DYNA. A comprehensive parametric study was carried out to investigate the effects of nine demand and design parameters on the performance of bridge columns. Studied parameters included: column diameter, column height, unconfined compressive strength, steel reinforcement ratio, fire duration, CFRP wrap thickness, wrapping configuration, vehicle 's mass, and vehicle 's speed. For each studied scenario, Peak Twenty-five Milli -second Moving Average ( PTMSA ) was employed to estimate the Equivalent Static Force ( ESF ) corresponding to each vehicle collision scenario. Resulting ESF s were then utilized to assess effectiveness of the current ESF approach available in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design ( AASHTO-LRFD ) Bridge Design Specification for analyzing and helping design bridge columns under vehicle collision. Multivariate nonlinear regression analyses were used to derive an empirically based, simplified equation to predict the ESF that corresponds to a vehicle collision. Rather than constant design force, this equation established a correlation between ESF and kinetic energy, column axial capacity, and column height. Results indicated that the proposed equation is reliable and can accurately predict ESF s over a diverse range of collision scenarios that included intact, fire damaged, and CFRP retrofitted columns. To facilitate realistic implementation of the derived equation, an ESF assessment framework was also devised.