Research on the impact performance of composite girders integrating corrugated steel web (CSW), concrete-filled steel tubular (CFST) chord, and ultra-high performance concrete (UHPC) slab remains limited, despite their growing application in mountainous bridges where rockfall hazards are prevalent. In this study, a high-fidelity finite element (FE) model in ABAQUS is developed to simulate the dynamic response of such composite girders under random rockfall impact. The model incorporates material nonlinearity, damage evolution, strain-rate effects, and reinforcement fracture, and is validated against existing experimental impact test data, demonstrating good agreement in terms of damage modes, impact force, support reaction force, and structural displacement. With the validated numerical model, parametric investigation is then conducted to reveal the dynamic response mechanisms, examining the influence of critical parameters, i.e., impact mass, impact velocity, rockfall geometry, rockfall size, rotational angular velocity, and impact angle. The results indicate that rockfall geometry and size predominantly affect the contact area, thereby governing the peak impact force. Increasing rotational angular velocity (from 0 rad/s to 60 rad/s) significantly aggravates localized damage in the UHPC slab and amplifies fluctuations in the impact force plateau by over 20%, while exerting a negligible effect (less than 5% variation) on global displacement. In contrast, impact mass and velocity govern the global structural deformation. Finally, by combining dynamic analysis with sectional capacity theory, a practical design equation for the bending moment amplification factor is derived via regression. The proposed formula predicts dynamic moment capacity with an error margin below 5%. This study provides essential insights and a design tool for impact-resistant composite bridges in mountainous areas.
Xian et al. (2026) studied this question.