Seismic Design of Lifeline Bridge using Hybrid Seismic Isolation

This paper presents the merits of a hybrid seismic isolation system used for the seismic design of a major bridge. The bridge is analyzed for two different arrangements of seismic isolation systems. The first arrangement consists of friction pendulum bearings at all substructure locations; the other incorporates a hybrid system where laminated elastomeric bearings are used at the abutments and friction pendulum bearings at the piers. Analysis results have demonstrated that the hybrid seismic isolation system provided a structure with a fundamental period long enough to attract smaller seismic forces, while controlling the magnitude of isolation bearings displacements. It also provided a more uniform distribution of seismic forces among substructure elements. As a result, higher seismic forces on the piers were reduced, allowing for a more economical design of substructures. The hybrid seismic isolation system helped to control the wind-induced vibrations and reduced the sizes of the isolation bearings.