The design and use of rubber bearings for vibration isolation and seismic protection of structures

Abstract

The development of rubber structural bearings for civil engineering applications is described. Rubber bridge bearings are designed to be stiff vertically and soft horizontally. Bearings with these characteristics can be designed from a knowledge of the compression characteristics of rubber blocks. A formula for the compression modulus in terms of the shape factor of the rubber block is given. Both natural and synthetic rubber (neoprene) are normally satisfactory; although stiffening of neoprene may occur where temperatures are at or below 0 degrees C for extended periods. Relevant static and dynamic properties of rubber and the extension of the design methods to provide seismic protection for buildings are described. For anti-seismic bearings the very low horizontal stiffness required may lead to a tall unstable bearing, and detailed consideration of this stability may be required. The possible buckling of the mount under the vertical load must also be considered. It is also important to select the correct degree of damping in the bearing material. (TRRL)