Dynamic response and damage assessment of steel box girder bridge under far-field blast loading

Steel box girder bridges are widely used in bridge structures due to their lightweight design, high strength, and rapid construction characteristics. However, during their service life, they may face the threat of long-duration, high-impact far-field blast waves caused by explosions in large-scale chemical industries, which can directly affect the structural safety performance. This study investigates the dynamic response and damage assessment of steel box girder bridges under far-field blast loads. To achieve this, a numerical simulation method combining Computational Fluid Dynamics (CFD) and Explicit Dynamics is proposed. The CFD method accurately simulates the complex interactions between far-field blast waves and bridge components, including diffraction and clearing effects, providing high-precision blast loads for dynamic response analysis. Research has found that the failure mode of steel box girder bridges is closely related to the incidence angle of detonation waves. When the incidence angle of the detonation wave is 0°, the damage to piers is primarily attributed to the impact force generated as the girder is uplifted and subsequently falls. At non-zero incidence angles, the primary failure mode of the bridge shifts to bending-shear damage of the girder. Furthermore, for a fixed incidence angle, the extent of bridge damage intensifies significantly with the increasing intensity of the far-field blast loads. This paper also assesses the damage caused by far-field explosions to steel box girder bridges based on probabilistic methods. The assessment results indicate that the failure probability of bridge piers decreases as the incident angle increases, whereas the failure probability of main girders rises with increasing incident angles. Moreover, the overall failure probability of the bridge system also shows an upward trend as the incident angle grows. The findings provide a theoretical foundation for analyzing dynamic responses, conducting damage evaluations, and formulating post-disaster strengthening measures.