Effect of girder-bearing separation on horizontal collision of shear keys under seismic excitations

This study investigates the impact of separation between girders and bearings on the collision response of shear keys under near-field seismic excitations involving both horizontal and vertical components. Based on continuum dynamics, structural displacement and collision equations are derived using the wave function expansion and mode superposition methods, and bridge collision limit-state solutions are established. The results indicate that vertical excitation significantly amplifies the horizontal collision force compared to cases where it is neglected. Moreover, vertical excitation induces an upward shift in the contact point between the girder and the shear key. This effect is exacerbated when the excitation frequency approaches the natural frequency of the structure, leading to more severe collisions. Numerical simulations validate the reliability of the theoretical model. The findings suggest that conventional shear key design practices, which often neglect vertical excitation, potentially underestimate the risk of failure. The proposed theoretical framework accurately quantifies the bridge’s seismic response and facilitates the assessment of critical collision scenarios using limit-state solutions, thereby contributing to the advancement of seismic design methodologies for shear keys.