Analysis of Experimental Investigations on Elastomeric Seismic Isolation Bearings

In this paper the main results of some experimental investigations on laminated rubber bearings, reported in the international technical literature or carried out in the Laboratory of testing materials and structures of the University of Basilicata, are critically reviewed and compared. The trends of shear stiffness and damping properties with respect to axial load and shear strain are analysed. Whereas experimental results show that shear stiffness depends strongly on shear strain, a clear influence of axial load on shear stiffness does not come out. Shear stiffness also depends on the loading history which is carried out. This influence can mask the role of other parameters such as, for instance, the level of axial stress, and shall be adequately taken into account when carrying out tests and/or when evaluating results. Analysis of energy-dissipating properties on the basis of equivalent viscous damping ratio and of normalised dissipative energy confirms that the former one does not effectively represent damping characteristics for highly non linear behavior.