Analysis of the Large Deformation Stability of Elastomeric Bearings
Publication: Journal of Engineering Mechanics
Volume 140, Issue 6
Abstract
Seismic isolation using multilayer elastomeric isolators has been used in the United States for more than 20 years. The isolators are constructed of many layers of elastomer (usually natural rubber) reinforced with steel plates, and they are very stiff in the vertical direction but soft in the horizontal direction, which enables them to carry the weight of a building but cause the building to have a fundamental natural frequency that is both lower than that of the same building if conventionally founded and the dominant frequencies of strong ground motion. They appear to be very stable, but the low shear stiffness causes a buckling phenomenon. However, it is straightforward to design them to have a large factor of safety against buckling when used. The study of the buckling under compression load is based on a linearly elastic theory and, although the elastomer is not really linearly elastic, the deformation is predominantly one of shear, and the typical elastomers used in bearings are very linear over a large range of strain. The linear theory, although approximate, is relatively accurate and is adequate for most design purposes. What is not known is the large deformation response of a bearing when buckling occurs. The question of the stability of the postbuckled state remains unresolved. In the analysis of dynamic response of structures on these isolators, it is also necessary to understand the interactions between horizontal stiffness and vertical load and between vertical stiffness and horizontal displacement and both the postbuckling compressive and tensile behaviors. All these effects can be derived by a simple two-spring model described in this paper.
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Acknowledgments
The authors thank Ente Cassa di Faetano and Banca di San Marino for supporting this study with Fondo per l'Eccellenza Sammarinese scholarship.
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Published In
Journal of Engineering Mechanics
Volume 140 • Issue 6 • June 2014
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Mar 25, 2013
Accepted: Oct 11, 2013
Published online: Oct 12, 2013
Published in print: Jun 1, 2014
Discussion open until: Jun 30, 2014
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