Stability Aspects of Elastomeric Isolators

Abstract

The theoretical analysis for the buckling of isolators is well known and has generally been verified by experimental work, but there are some aspects of the analysis that have not been addressed in detail. This paper will study two examples, first the effect of end plate rotation on the buckling load and, secondly, the buckling of an isolator that is made up of two bearings, one on the top of the others. The effect of end plate rotation on the buckling load arises in situations where the stiffness of the superstructure is not high enough to ensure that the isolator is constrained against rotation at the top; this is often the case when retrofitting existing structures. The influence of the flexibility of the superstructure on the horizontal stiffness of the isolator and the reduction of the critical load due to this flexibility is evaluated in the paper. The results show a significant reduction of the critical load. The second analysis presented in the paper models the buckling of a composite isolator that is made up of two bearings, one on top of the other. Two approaches for evaluating the critical load of this composite isolator are discussed, and an approximate method is developed that provides results close to the complete solution.