Free vibration problem of PRSI bridges: analytical solution and parametric analysis

This paper analyzes the dynamic behavior of partially restrained seismically isolated (PRSI) bridges. These are a particular class of multi-span seismically isolated bridges in which isolation bearings are posed only at the top of the piers, while seismic stoppers restrain the transverse motion of the superstructure at the abutments. The transverse dynamic behavior of these partially-restrained bridges is described analytically by considering a two-dimensional simply supported beam model, with intermediate visco-elastic restraints whose properties are calibrated to describe the substructures’ behavior. Particular simplified configurations are considered which allow to identify a minimal set of characteristic problem parameters that completely describe the dynamic response. The properties of the dynamic systems are analyzed by considering separately the undamped and the damped case. The results of the study contribute to improve the understanding of the dynamic behavior of partially restrained seismically isolated bridges and allow to draw some conclusions useful for their preliminary assessment and design.