Seismic Analysis of the Hybrid Rocking Bridge Bents

Current (code-based) seismic bridge design focuses on accommodating structural deformation, and eventually damage, during an earthquake excitation. On the contrary, a rocking bridge pier/bent is designed to uplift and pivot, in order to limit structural deformation and damage. A rocking bridge utilizes primarily its rotational inertia to counter the seismic demand. This paper investigates, analytically and numerically, the seismic response of a symmetric rocking bridge bent/frame. In particular, it examines both free-standing and hybrid (i.e. enhanced with supplemental damping and re-centering capacity) symmetric rocking bridge bents. The paper neglects the structural deformation of the frame-members and establishes the equations of motion following the principles of analytical dynamics. The analysis considers both pulse-type and non-pulse-type ground motions. It illustrates the sensitivity of the response to the fracture elongation of the supplemental re-centering and damping devices. The results confirm the high-performance seismic behavior of the (hybrid) rocking frame.