Stability issues and pressure–shear interaction in elastomeric bearings: the primary role of the secondary shape factor

Stability of isolation rubber bearings is a topic widely studied and concerns (1) the critical load capacity in the undeformed configuration, under long-term load (gravity) effects; and (2) the stability condition under short-term vertical pressure (due to gravity plus seismic loads) at large lateral deformations. In this paper the problem of elastomeric bearing stability under large lateral displacements is addressed through FEM parametric analysis; rubber bearings typical of current design practice, characterized by S1 = 20 are considered, with the value of the secondary shape factor S2 being varied between 1.5 and 6.2 in order to assess the effect of slenderness on the mechanical behavior, failure mode, and interaction vertical pressure–shear deformation. The analysis results show that the sensitivity of the shear response to the applied vertical pressure is directly related to the value of S2 and that S2 has an overwhelming effect on the stability behavior and shear response of the bearing, as compared to the effect of the primary shape factor and of the rubber shear modulus. Finally, S2 is the parameter which governs the failure mode of the bearing in the seismic condition (vertical pressure–shear deformation). On the basis of these results, design implications are discussed.

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