Seismic performance of bridge isolated by FPS

The aim of this work is to evaluate the optimal properties of friction pendulum system (FPS) bearings for the seismic protection of a bridge pier under earthquake excitations having different frequency characteristics representative of different soil conditions. The response of the system is described through a two-degree-of-freedom model, considering an infinitely rigid deck isolated by the FPS devices and an elastic behavior of the pier. A widespread velocity-dependent model is adopted to illustrate the FPS isolator behavior. The influence of different structural parameters on the isolated bridge response has been investigated, performing a wide parametric analysis, by means of a non-dimensional formulation of the motion equation. Seismic excitations herein considered are modelled as time-modulated filtered Gaussian white noise random processes having different intensities and frequency contents. In particular, the filter parameters, which control the frequency contents, are properly calibrated to reproduce stiff, medium and soft soil conditions, respectively. Finally, optimum values of the sliding friction coefficient have been computed, able to minimize the pier displacements relative to the ground depending on the structural properties, on the seismic input intensity and on the soil condition.