INFLUENCE OF MATERIAL STIFFENING ON STABILITY OF ELASTOMERIC BEARINGSAT LARGE DISPLACEMENTS

Experiments conducted to determine the mechanical characteristics of l ow shape factor bearings demonstrated that low shape factor elastomeri c bearings that were bolted to their endplates-as opposed to bearings with doweled-type endplate connections-showed an increase in horizonta l stiffness at large shear strains. This strain-induced crystallizatio n at large shear strains offers a good reserve of shear resistance for bearings subjected to large deformation, thereby providing a high saf ety factor against failure under earthquake loads that exceed the desi gn level. Modeling this property would be invaluable for structural en gineers designing isolators for use in highly seismic areas. This pape r presents an analytical method that adequately models the strain-indu ced crystallization of the elastomer at large shear strains. This mode l 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 ru bber is taken into account by replacing the shear modulus, G, by a she ar modulus-shear strain relationship and calculating the shear strain from a root mean square average of the shear strains of the elastomeri c bearing that is due to compression, bending, and shearing.