The Properties of Lead-Rubber Bearings Including the Influence of Varying Vertical Load Under Severe Conditions

Abstract

The widespread use of seismic isolation has necessitated a better understanding of the more complex aspects of isolation device behavior. The properties of seismic isolation devices depend upon the interaction between horizontal and vertical forces acting on the isolator. The actual hysteretic behavior of an isolation bearing under a structure subjected to severe earthquake shaking is influenced by the variation of vertical load on the isolator due to overturning forces. To identify the mechanical characteristics of lead-rubber isolators, cyclic shear tests of isolators under varying vertical load were conducted. The authors propose an analytical model for predicting the behavior of isolators under varying vertical load conditions. The model can reflect the influence of varying vertical load on isolator properties, and this capability is confirmed by simulation analyses and comparison with the cyclic shear test results. The analytical model is also used to investigate the behavior of lead-rubber isolators under loadings more severe than typical design conditions.