Modification of Existing Models To Include the Effect of Rotation on the Behavior of Elastomeric Bearings

Abstract eng:
Seismic isolation is a design approach that aims at reducing earthquake demands on a structure and its contents. Conventional practice places the isolation system at the foundation level and calls for the construction of rigid diaphragms above and below the isolation layer. Consequently, these rigid diaphragms prevent the isolators from experiencing rotation, and the isolators displace horizontally and vertically only. However, there are several scenarios where isolators do experience rotations, including in tall buildings, in mid-story isolation applications, in bridges, etc. Various mechanical models have been proposed to investigate the horizontal behavior of elastomeric isolators under the assumption of zero top and bottom rotation. Those studies have characterized the effect of vertical load on the lateral stiffness and the lateral stability limit (defined as the displacement at which the tangent stiffness becomes zero). In this study, three existing models are considered: the Nagarajiah-Ferrell, Iizuka, and Han-Warn models. First, these three models are evaluated by comparing their predictions to results of Finite Element Analysis (FEA), assuming no rotation at the supports. Then, the models are modified to account for the effect of rotation. The modified models are evaluated using results from FEA under prescribed rotation values. The results show that the Han-Warn model provides more accurate predictions than the Nagarajiah-Ferrell and Iizuka models.

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