Dynamic response and damage mechanism of reinforced concrete beam bridges under rockfall impacts

In the first phase, this study references previous beam impact tests and uses Abaqus to create a finite element model for beams. Then the feasibility and accuracy of the concrete plastic damage model in analyzing the response of reinforced concrete structures under impact loads were validated. In the second phase, a detailed numerical model was developed using Abaqus to examine the dynamic response and damage mechanism of prestressed concrete simply supported box girder bridge with a 30 m span and high piers. The analysis considered a single rockfall impacting the pier at various heights and multiple rockfalls of varying radius and velocities hitting the bridge successively. Results showed that under a single rockfall, both the peak bending moment and shear force occurred at the point of impact. The shear force at the upper section of the impacted pier was significantly higher than at the lower section. For multiple rockfalls, the maximum bending moment occurred at the first impact location, followed by the second, with nearly identical shear force peaks for both. When comparing single and multiple rockfall impacts, the first impact influenced the second's peak period, but the second did not affect the first. Bridge damage analysis revealed severe compressive damage at the impact site in both scenarios, with concrete failure and exposed reinforcement observed on the inner side of the impact points. Tensile damage was more pronounced under multiple rockfall impacts. Parametric analysis showed that while impact height had little effect on the peak impact force, the peak bending moment and shear force varied significantly with height. The peak impact force, horizontal displacement, bending moment, and shear force increased with rockfall velocity and radius in multiple impacts. The analysis results indicate that the dynamic response and the damage of beam bridges under rockfall impacts are highly related to the connection joints, which must be given special attention during bridges design. Damage assessment methods indicated minor damage when the pier was impacted by rockfalls with a 0.5 m radius, but severe damage occurred at a velocity of 40 m/s, with moderate damage in other cases. Finally, some analysis results can provide important references for the bridges of the same type. Meanwhile, this study can also provide a useful reference in design and restoration of reinforced concrete beam bridges located in areas prone to frequent geological disasters.