Some observations in the seismic response of isolated bridges with abutment transverse restraint

This paper analyzes the dynamic behavior of seismically isolated bridges with abutment transverse restraint. These are a particular class of multi-span bridges in which isolation bearings are posed only at the top of the piers, with seismic stoppers restraining the transverse motion of the superstructure at the abutments. The bridges are modeled by two-dimensional simply supported beams with intermediate visco-elastic restraints, whose properties are calibrated to describe the behavior of the substructures. Particular simplified configurations are considered which allow to identify a reduced set of characteristic parameters controlling the response. The closed form analytical solution for the free-vibration and seismic problem is illustrated, first. Then, the seismic response of a four-span isolated bridge with a steel concrete composite deck restrained at the abutments is investigated. A parametric analysis is performed by varying the intermediate supports stiffness and dissipative properties and by analyzing the changes in the modal properties and in the seismic response. The analysis of the case study permits to shed light on important aspects of the dynamic behavior of the class of bridges considered.