Behavior of elastomeric seismic isolators varying rubber material and pad thickness: A numerical insight

A numerical approach for the determination of (a) the shear behavior under large displacements and (b) the compression elastic modulus of common parallelepiped elastomeric isolators is presented. Particular attention is devoted to the role played by the material used for the rubber pads and their thickness. For them, an experimental data fitting by means of both a nine constants Mooney-Rivlin and a five constants exponential law is utilized, within a Finite Element discretization of the isolator. Having at disposal a few experimental stretch-stress data points for each rubber compound in uniaxial tension, a cubic Bezier spline approach is firstly utilized, to generate numerically a large number of metadata containing the original experimental ones. Then, respectively the nine Mooney-Rivlin and five exponential law constitutive parameters are estimated through a least square approach. Once assessed the models, a full scale rectangular seismic isolator is analyzed when subjected to horizontal actions and normal compression, in order to provide estimates of the initial stiffness and the overall behavior of the isolator undergoing large deformations, using both models and for all the compounds considered. It is found that the global behavior may depend significantly on the material hypothesis assumed to model rubber and on pads thickness.