Effect of Side Retainers on Seismic Response of Bridges with Elastomeric Bearings

Often, to restrain the lateral displacement of elastomeric bearings in slab-girder bridges, two retainers in the form of angles or welded plates are placed on each side of the bearings, with a slight clearance to allow for longitudinal movement of the elastomer. The existence of the gap introduces nonlinearity into the seismic analysis of the structure, which is commonly ignored. In addition, by considering the gap, the elastomer’s stiffness in the transverse direction contributes to the overall stiffness of the system. This paper investigates the behavior of these retainers under earthquake forces. The retainers’ stiffness, the gap distance, and the period of the bridge are used as variable parameters. It is shown that the seismic demand on retainers is nonlinear in nature and depends on the frequency content of the input motion. It is also proved that ignoring the gap in the seismic analysis model can lead to lower seismic demands on the retainers and substructure. Design recommendations are given for bridges with such retainers.