Dynamic response and failure mechanism for urban continuous beam bridges under far-field blast loads

Urban bridges are frequently exposed to blast threats arising from accidental explosions and terrorist attacks. However, existing studies on bridge responses under blast loading remain limited, particularly for far-field blast conditions. To investigate the dynamic response and damage mechanisms of urban continuous beam bridges subjected to far-field blast loading, LS-DYNA was employed to efficiently apply blast loads and perform numerical simulations accounting for blast-induced fluid-structure interaction. Based on a typical continuous beam bridge, a refined numerical model was developed to analyze the response process and representative damage modes of the bridge under different blast scenarios. Furthermore, the effects of blast distance, explosive charge weight, and impact angle on structural response and damage were systematically examined. The results indicate that, under far-field blast loading, the continuous beam bridge exhibits a global structural response, with uplift of the superstructure and tilting of the bridge piers being the dominant characteristics. The uplift of the superstructure is primarily influenced by the blast load and the spatial geometric characteristics of the bridge, whereas the tilting of the piers is associated with the direct action of the blast wave and the displacement of the superstructure. Under perpendicular impact, typical damage modes include wet joint failure, flexural deformation of box girders, crushing damage at the tops and bases of piers, and bending cracks in bent caps. Under oblique blast loading, torsional deformation of pier columns is additionally observed in the substructure. A decrease in the impact angle or the scaled distance results in an increase in the overall damage of the bridge structure. Evaluation based on the proposed weighted damage factor indicates that, compared with the impact angle, the overall damage of the continuous beam bridge is more sensitive to variations in the scaled distance. The findings of this study provide useful analytical approaches and mechanistic insights for understanding blast responses and guiding the blast-resistant design of bridge structures.