Impact Characteristics and Parameter Analysis of Collisions Between Oversized Vehicles and Steel Bridge Girders

To address the insufficient dynamic quantification of instantaneous impact loads when overheight vehicles impact steel bridge girders, as well as the potential limitations in applicability and safety reserve of current static design values in existing codes, this study establishes a nonlinear finite element model for overheight vehicle impact on steel bridge girders and verifies the rationality of the model parameters. The impact dynamic responses and parameter sensitivity laws of steel bridge girders subjected to three typical types of overheight cargo are analyzed under different impactors, impact locations, and impact velocities. By examining the characteristics of impact force time histories, statistical patterns, and main influencing factors, the variation laws of impact force with impactor properties, impact location, and impact velocity are revealed. The results show that both the peak and average impact forces increase with increasing velocity. When the velocity increases from 48 km/h to 144 km/h, the amplification factor of the average impact force is approximately 2.0. As the plastic development of the impactor and the impacted component increases, the growth rate of the impact force slows down to varying degrees. The impact force time histories differ significantly among different impactors. Due to differences in impactor stiffness, the coupled force-transfer evolution and plastic development behavior between the impactor and the steel bridge girder vary, resulting in different impact durations. Among them, the concrete duct has the shortest impact duration due to brittle failure, approximately 0.05 s, while the fully loaded semi-trailer has the longest duration due to flexible buffering, ranging from 0.13 s to 0.15 s. The actual impact force ranges from 396 kN to 1504 kN, with the upper limit significantly exceeding the 500 kN static design value recommended by EN 1991-1-7 Eurocode 1. This indicates that using a unified static design value may underestimate the impact loads acting on steel bridge girders and may lead to insufficient structural safety reserve. The findings of this study can provide a reliable quantitative basis for impact-resistant design of steel bridge girders, safety assessment of existing bridges, and optimization of anti-collision protection measures.