Dynamics and seismic stability of planar symmetric rocking bridges

This study explores analytically the concept of rocking isolation in bridges with a view to establishing the suitability of this configuration when used in regions with high seismicity. Adopting the assumption that the deformation of the structural members is negligible, the dynamics of a rocking bridge with free-standing piers of same height and section (symmetric) are derived, considering for the first time the influence of the abutment. The formulation includes the combined effect of a spring and dashpot element in the longitudinal direction and two additional supports in the vertical one. A new parameter that depends on the bridge properties is introduced (q_abut.) to account for the contribution of the abutments to the dynamic response. Energy dissipation is expressed through the restitution coefficient; a new expression for this parameter is derived, showing that the redistribution of the deck weight due to the support at the abutments leads to lower energy dissipation compared to that of the corresponding frame model used so far. The results show that the abutments have a generally beneficial effect on the seismic performance of the bridge in terms of both peak and overall responses; nevertheless, more impacts occur compared to the rocking frame, pointing to the special attention needed for detailing the rocking interfaces.