Three‐dimensional analysis for square seismic isolation bearings under large shear deformations and high axial loads

Abstract

Square seismic isolation bearings are economical to manufacture, offer the advantage of simple connection configurations and have compact geometry requiring a minimum of space for installation. To be able to more effectively utilize square bearings for seismic isolation systems, a new mechanical model for predicting the large shear deformation behavior of square elastomeric isolation bearings is presented in this paper. The new model is developed by extending to three dimensions an existing model for elastomeric isolation bearings under severe axial loads and shear deformations. The model comprises multiple shear springs at the mid-height and a series of axial springs at the top and bottom boundaries. Static loading tests of square lead-rubber isolation bearings were performed to investigate the influence of horizontal loading direction and axial load magnitude on bearing behavior. The test results showed that the ultimate behavior is strongly influenced by loading direction, especially under large shear deformation and high axial load. To confirm the validity of the model, analyses are performed of the loading tests of the square lead-rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results.

A Review of Seismic Isolation for Buildings: Historical Development and Research Needs

“…A model that includes the influence of vertical load on the effective horizontal stiffness and lead-core yield strength was developed by Ryan et al [35] and has been implemented in OpenSees [26]. Models that account for the second-order effects due to vertical load at large horizontal displacement have been developed [36][37][38] and are capable of exhibiting zero or negative tangential horizontal stiffness as has been experimentally demonstrated [39]. However, these models have not been widely adopted due to the extensive experimental data required to calibrate the model parameters.…”

Improved numerical analysis for ultimate behavior of elastomeric seismic isolation bearings

“…Figure shows nonlinear hysteretic models used for the multiple springs. These are models that have previously been proposed for lead‐rubber bearings . The axial stress‐strain relationship shown in Figure A exhibits high stiffness and yielding stress in the compression region and low stiffness and yielding stress in the tension region.…”

“…This model is an extension of the mechanical model proposed by Yamamoto et al and Kikuchi et al The improved model proposed herein is specific to circular bearings and considers the compression modulus distribution with a minimal increase in complexity. In other words, the mechanical model proposed by Yamamoto et al for 2‐D analysis without considering the modulus distribution has been upgraded to a 3‐D model considering the modulus distribution, and the mechanical model proposed by Kikuchi et al for square bearings has been modified using the proposed grid pattern and modulus distribution for circular bearings. A detailed model formulation that considers finite deformations and the P‐Δ effect was described in the preceding paper .…”

“…In other words, the mechanical model proposed by Yamamoto et al for 2‐D analysis without considering the modulus distribution has been upgraded to a 3‐D model considering the modulus distribution, and the mechanical model proposed by Kikuchi et al for square bearings has been modified using the proposed grid pattern and modulus distribution for circular bearings. A detailed model formulation that considers finite deformations and the P‐Δ effect was described in the preceding paper . A brief explanation of the function of the components of model is given next.…”

“…A number of extensions of this extended model have been developed; for example, Ryan et al extended it further for lead‐rubber bearings by introducing nonlinear shear springs . Kikuchi et al proposed a multispring mechanical model that has two series of axial springs instead of the aforementioned rotational springs . The series of axial springs can account for nonlinear behavior in the rotational direction influenced by compressive load, which causes buckling under large shear deformation.…”