Assessment of Seismic Retrofit Measures for Bridge Bearings

The bridge model is quite sensitive to the change in stiffness as governed by the bearing stiffness. The analytical bridge model shows the stiffness of the bearings to be the most flexible (smaller stiffness value) element within the system, thereby controlling the response of the system. From the analyses of the Northridge ground motion, the rocker bearings reveal larger displacements for which toppling is probably occurring in the model and actually occurred on some bridges as a result of the earthquake. The friction pendulums tend to increase the stiffness of the system, thereby allowing the model to not be as susceptible to lateral displacements. Recommendations addressing inadequate seat widths due to large displacement demands are determined from the analyses. The toppling of the rocker bearings may occur when longitudinal movement exceeds the seat width, where an increase of the bearing stiffness should be applied using restrainers or other types of retrofit measures or the seat width should be increased to prevent toppling.