Mechanistic model for simulating critical behavior in elastomeric bearings

When an elastomeric bearing is subjected to simultaneous vertical compressive load and lateral displacement, the shear force can pass through a maximum beyond which the bearing exhibits negative tangential horizontal stiffness and a condition of unstable equilibrium. This behavior has been experimentally demonstrated and has important implications on the stability and earthquake response of elastomeric seismic isolation bearings. Yet, analytical bearing models used for numerical earthquake simulation assume a positive second-slope stiffness irrespective of vertical load and/or bearing lateral displacement and therefore are unable to simulate the experimentally observed bearing behavior. Semiempirical bearing models have been developed and some of these models have been shown to simulate the influence of vertical load and lateral displacement on the shear force response with reasonable accuracy, however these models rely on a number of experimentally calibrated parameters, making them impractical for the purpose of design. An alternative approach to modeling the behavior of elastomeric bearings is explored in this study, which uses a series of vertical springs and a simple bilinear constitutive relationship to represent the rotational behavior of elastomeric bearings. The mechanistic bearing model, utilizing vertical springs, is shown to be capable of simulating the experimentally observed behavior with reasonable accuracy without relying on experimentally calibrated parameters.