SUMMARYFor the purpose of predicting the large-displacement response of seismically isolated buildings, an analytical model for elastomeric isolation bearings is proposed. The model comprises shear and axial springs and a series of axial springs at the top and bottom boundaries. The properties of elastomeric bearings vary with the imposed vertical load. At large shear deformations, elastomeric bearings exhibit stiffening behavior under low axial stress and buckling under high axial stress. These properties depend on the interaction between the shear and axial forces. The proposed model includes interaction between shear and axial forces, nonlinear hysteresis, and dependence on axial stress. To confirm the validity of the model, analyses are performed for actual static loading tests of lead-rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Seismic response analyses with the new model are also conducted to demonstrate the behavior of isolated buildings under severe earthquake excitations. The results obtained from the analyses with the new model differ in some cases from those given by existing models.

The paper describes a new analytical model for predicting the large displacement behavior of square lead-rubber isolation bearings. The present model is developed by extending to three dimensions an existing model for elastomeric isolation bearings under severe axial loads and shear deformations. Static loading tests of square lead-rubber bearings are performed to investigate the effect of loading direction on bearing behavior. The test results showed that the ultimate behavior is strongly influenced by loading direction, especially for large shear deformation and high axial load. The results of analyses using the new model show very good agreement with the experimental results. Keywords : Seismic isolation, Lead-rubber bearing, Large deformation, Axial force, Non-linear hysteresis model

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Performance of the super high-rise seismically isolated building during the Great East Japan Earthquake was reported. The response acceleration of the top floor was almost same as that of the 1 st floor. The maximum displacement of the isolation devices was 15 cm, and the cumulative displacement was about 10 m. The dynamic response analysis, considered variation of the characteristic of rubber bearing, ambient temperature and so on, was coincident with observed records.