Analytical Modeling of Elastomeric Isolation Bearings under Severe Axial Load and Shear Deformations

Abstract eng:
This paper presents a new analytical model for elastomeric seismic isolation bearings. Elastomeric isolation bearings exhibit stiffening or buckling behavior influenced by the applied compressive stress under large shear deformations. The isolator properties depend on the interaction between the horizontal and vertical forces on the isolator. A new analytical model has been developed to predict the behavior of elastomeric isolators under high vertical loads and large shear deformations. The model includes the interaction between horizontal and vertical forces as well as the nonlinear hysteresis characteristics of elastomeric isolators at large shear deformations. The model captures isolator behavior due to varying vertical load, which is a necessary feature to accurately predict the influence of building overturning on isolation system response in an earthquake. To validate the model, simulation analyses of cyclic shear tests of lead-rubber bearings under constant and varying vertical load and cyclic shear deformations were conducted. The hysteresis loops obtained from the tests under constant compressive stress exhibited shear stiffening behavior for low compressive stress, with deterioration of horizontal stiffness under high compressive stress. The varying vertical load test hysteresis loops were not symmetric, rather they showed both stiffening behavior and a deterioration of horizontal stiffness depend on the level of vertical load. These test results show that compressive load strongly influences the shape of the shear hysteresis loops. The results of the analyses using the new model show very good agreement with both the constant and varying vertical load experimental results.

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