Title: Design Guidelines for Lead-Filled Elastomeric Bearings for Use in Seismic Isolation of Bridges
Author(s): T. Kelly and I. Buckle
Publication: Symposium Paper
Appears on pages(s): 551-576
Keywords: bridge bearings; earthquake-resistant structures; elastic properties; energy dissipation; isolation; lead (metal); rubber; structural design; Design
Elastomeric bearings have long been used for bridge structures to provide thermal movements and girder rotations under service loads and in building structures to isolate them from ambient vibrations. By increasing the total rubber thickness and by inserting a lead plug for energy dissipation, the function of the bearing may be extended to provide seismic isolation of bridges. Seismic isolation is a design concept that reduces earthquake forces by factors of up to 10, thus greatly enhancing the seismic resistance of the supported structure. This paper provides design guidelines to enable lead-rubber bearings to safely and efficiently act as seismic isolators and reviews the mechanical properties of lead-filled elastomeric bearings. Factors affecting the elastic and postelastic properties are listed, and other design-related parameters are described. A set of design procedures to incorporate the lead-rubber bearings for bridge structures is presented. These procedures include the determination of plan size to support gravity loads, the rubber thickness to provide the required flexibility, and size of the lead core to provide energy dissipation. The procedures are applicable for areas of low and high-seismic risk. The application of the procedures is illustrated by use on a seven-span bridge.