Abstract

Seismic isolation is a proven strategy for protecting critical infrastructures from the damaging effects of design-level earthquake shaking. For seismically isolated highway bridges, the expected seismic performance is to provide limited service under a safety evaluation-level ground shaking with minimal to moderate damage. The behavior under extreme shaking, corresponding to a large return period seismic hazard, is not well understood and could induce significant damage. In these rare events, the seismic isolation system can be subjected to displacement demands beyond its design capacity, resulting in failure of the bearings or exceeding the clearance and pounding against the abutment backwalls. To better assess the seismic performance of a prototype highway bridge subjected to earthquakes beyond design considerations, this study examines the bridge lateral displacement, the transfer of forces to the substructure, and potential failure modes of seismically isolated bridges. Advanced modeling approaches are considered to capture bearing characteristics such as hardening for large strain, and a pounding macro-elements is implemented. Results show that for beyond design shaking, the bearings can reach the maximum shear strain capacity, significant residual deformation of the abutment can result from pounding, and the columns can experience moderate damage. The progression of damage is identified and interpreted to assess downtime.