Seismic performance of highway bridges

The seismic response of both isolated and non-isolated highway bridges is investigated with the objective of determining the effect of some of the design parameters on the bridge response. A dynamic bridge model is used to compare the effect of various energy-dissipating concepts when the bridge is subjected to moderate to severe earthquake ground motions. The seismic energy is assumed to be dissipated by the inelastic pier behaviour or by the use of base-isolation devices such as the lead-rubber bearing system.It was found that allowing the pier to deform inelastically requires very high ductility design. Structural damage in the form of permanent deformation is unavoidable. The use of lead plugs in the isolation devices is a very efficient energy dissipation system. Selecting the force required to yield the lead plugs to be 5% of the superstructure's weight provides a reasonable balance between reduced shear force transmitted to the pier and increased displacement of the bridge deck. It was also concluded that the shearing force in the pier can be substantially reduced by locating the lead plugs at the abutments only.