Simplified transverse behaviour of partially isolated bridges

Seismic isolation is a widely diffused technique for the seismic protection of bridges. It usually consists on the introduction of isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake. Partially restrained seismically isolated continuous bridges are a particular class of isolated bridges whose transverse motion is restrained at the abutment, in order to avoid the use of expensive bi-directional joints. The present work describes a simplified method for the evaluation of the seismic response of these bridges which considers the dynamic problem in a variational form and seeks a simplified solution by assuming a sinusoidal transverse deformed shape. Simple formula are derived for estimating the displacement demand, the internal action demand at the piers and at the deck and the abutment reactions. Some validation studies are also carried out in order to evaluate the accuracy of the proposed method in assessing the response of these systems.