SACRIFICIAL BEARING COMPONENTS FOR QUASI-ISOLATED RESPONSE OF BRIDGES SUBJECT TO HIGH-MAGNITUDE, LOW-PROBABILITY SEISMIC HAZARD BY

ii Bridges in low- to moderate-seismic zones, such as Mid-America, commonly employ elastomeric expansion bearings to accommodate service-level thermal deformations in the superstructure. Any potentially beneficial effect of these bearings during seismic loading is typically ignored, and the surrounding substructure or superstructure is designed to accommodate the seismic demands through traditional means of ductile plastic response. This scenario presents an opportunity for bridge designers, particularly in these geographical regions (and potentially for all seismic zones). If the elastomeric bearings can reliably be depended upon to provide reduced transmissibility of ground motion excitation to the superstructure, then the structure can be said to be partially isolated, or “quasi-isolated”. This study explores the potential benefits and applicability of sacrificial bearing components (i.e., “fuses”) for bridge structures subjected to seismic effects. Fundamentally, a design paradigm embracing such components requires that two disparate objectives are met. First, the bearing fuses must perform with predictable, reliable response for service loading conditions, including small earthquakes