Bridge bearing fuse systems for regions with high-magnitude earthquakes at long recurrence intervals

This paper describes an ongoing experimental and computational program investigating bridge bearing assemblies common in mid-America, to ascertain their effectiveness as seismic fuses and to characterize their component behavior during large displacements of the superstructure. The bearing assemblies considered in the testing program are intended to address seismic risk for regions where the hazard is dictated by infrequent, but large magnitude, seismic events such as may occur in the New Madrid seismic zone near southern Illinois. Test specimens include low-profile fixed bearings, as well as steel-reinforced elastomeric bearings. The elastomeric bearings, some of which include a Teflonon- steel sliding surface, have stiffened L-shaped retainer brackets to restrain transverse response at service load levels. The bearing components being studied are intended to ensure predictable, elastic response for service loading, including small seismic events. However, for larger seismic events, mechanical response of these bridge bearings will transition through highly nonlinear mechanisms that require a refined behavioral understanding, including post-yield deformations and fracture of selected steel components in the fixed bearings, high shear strain response in the elastomer, and sliding along predetermined interfaces. The experimental program is evaluating potential fuse mechanisms and component behavior that will then be implemented in computational models of complete bridges to assess global system response. The research will develop comprehensive test data upon which to base bridge design guidelines for proportioning fuse components to provide reliable service performance, as well as a passive, quasi-isolated global response during a major seismic event. This design dichotomy of bridge response ensures seismic safety (i.e., prevention of span loss) while maintaining appropriate fiscal responsibility consistent with the nature of seismic risk in regions where major earthquakes are expected to occur only at long recurrence intervals.