Quantification of fuse capacity for elastomeric and low-profile steel fixed bridge bearings in regions with high-magnitude earthquakes at long recurrence intervals

Bridge designs in regions with moderate seismic hazard can be relied upon to provide an effectively isolated response and to protect super- and substructure components when the force transmission characteristics of the bearing components are properly accounted for in design and analysis. An experimental program for common bearing configurations employed in the state of Illinois investigated the peak capacity and transition mechanisms expected for non-seismic bearings subjected to seismic demands. Horizontal fuse capacity for elastomeric bearings ranged from about 0.2 to 0.6 times the bearing vertical gravity load when relying solely on friction between elastomer and concrete, and increased to about 0.7 to 1.0 in the bridge transverse direction due to stiffened angle retainer brackets anchored to the concrete substructure. The presence of polytetrafluroethylene (PTFE) decreased the fuse capacity to about 0.1 to 0.15, even accounting for contamination of the slip surface and velocity-dependence, and to about 0.4 to 0.75 with retainers in the transverse direction. Steel fixed bearings anchored to concrete demonstrated fuse capacities of about 0.85 to 1.15 prior to rupture of the anchors securing the bearings to the substructure, and subsequent coefficients of friction of about 0.2 to 0.4. These values consistently exceeded a target fuse limit of 0.2 times gravity load, as selected by the Illinois Department of Transportation. The experiments demonstrated that if fuses are intended to be used as part of an Earthquake Resisting System, performance of the components must be carefully considered and designs must be calibrated to ensure satisfactory response of the entire bridge structure.