Tension buckling in rubber bearings affected by cavitation

Abstract

Multilayer laminated rubber bearings are the most common antiseismic devices, typically used to isolate buildings. They are made with steel reinforcing layers that provide a vertical stiffness several hundred times the horizontal one. Although these bearings appear to be very stable, they face a buckling phenomenon, caused by low shear stiffness, that needs to be investigated.In particular cases, seismic codes might require that bearings take some amount of tension that should be contemplated in the design. Several studies demonstrated that the buckling analysis for compression leads to the prediction that the isolator can buckle in tension at a load close to that for buckling in compression.Moreover, the predicted tensile buckling load is in general, not achievable, since the elastomer in tension experiences cavitation at relatively low tension stresses. However, numerical simulations have shown that tensile buckling in multilayer elastomeric bearings is also possible in the absence of cavitation.In this paper an analytical formulation to predict the instability of a rubber bearing affected by cavitation is elaborated. A procedure to calculate buckling load in tension in the presence of cavitation is developed for both long strip bearings and circular bearings. The analysis is conducted by using an analytical model that describes the effects of cavitation on both compressive and bending stiffness of rubber bearings used for antiseismic purposes.