A design method for seismically isolated bridges with abutment restraint

Seismic isolation is a commonly used technique for protecting new and existing bridges. It usually consists of introducing isolation bearings between the superstructure and the substructures in order to decouple their motion and reduce the force demand due to the earthquake action. This paper deals with partially restrained seismically isolated continuous bridges, which are a particular class of isolated bridges whose transverse motion is restrained at the abutments.In this study a method is proposed for the preliminary design of these systems, which can be applied to both new and existing bridges. The dynamic problem is described in a variational form in order to obtain a simplified solution based on a pre-fixed transverse deformed shape of the deck. The objective of the design procedure is to control the internal actions on the piers by means of an appropriate configuration of the isolation bearings. Simple formulas for estimating the forces transmitted to the abutments and the superstructure transverse curvature demand are also derived, which account for the contribution of higher modes of vibration.Validation studies are undertaken for different bridge configurations, in order to assess the ability of the simplified method to control the force demand at the piers.