Dynamic interaction of bridge spans and piers as a tuned system for seismic load reduction

Bridges located in seismic regions are subjected to strong dynamic actions that may cause excessive bending moments, shear forces, and displacements in piers and foundations. In conventional seismic design, the bridge span is commonly treated as a rigid inertial mass transmitting earthquake-induced forces to the supports, while the beneficial dynamic interaction between the span and the pier is not fully utilized. This study proposes a seismic protection approach in which the bridge span is considered as a tuned dynamic component capable of reducing the response of the pier. A coupled two-degree-of-freedom mathematical model of the span–pier system subjected to base excitation is developed, and a parametric analysis is carried out to determine rational stiffness and damping parameters of the span–support connection. The optimization procedure is performed under practical displacement constraints imposed by the deformation joints. The results show that the most efficient vibration reduction is achieved for properly selected stiffness and damping ratios, with the practical stiffness range lying near f = 0.12 and f = 0.2-0.3, depending on the adopted damping level. For the considered bridge, the permissible relative displacement of the span with respect to the support is 6-12 cm, and the bending moments in the pier can be reduced by up to 2.33 times compared with the conventional seismic design approach. The proposed method improves the seismic reliability of reinforced concrete bridge systems without introducing additional external damping masses.