Influence of Material Stiffening on Stability of Elastomeric Bearings at Large Displacements

Abstract

Experiments conducted to determine the mechanical characteristics of low shape factor bearings demonstrated that low shape factor elastomeric bearings that were bolted to their endplates—as opposed to bearings with doweled-type endplate connections—showed an increase in horizontal stiffness at large shear strains. This strain-induced crystallization at large shear strains offers a good reserve of shear resistance for bearings subjected to large deformation, thereby providing a high safety factor against failure under earthquake loads that exceed the design level. Modeling this property would be invaluable for structural engineers designing isolators for use in highly seismic areas. This paper presents an analytical method that adequately models the strain-induced crystallization of the elastomer at large shear strains. This model extends the linear elastic relationship developed in earlier studies to predict the buckling load of an elastomeric bearing in the case of material nonlinearity. Here, the nonlinear elastic response of the rubber is taken into account by replacing the shear modulus,