To realistically reproduce experimental results, a hysteresis behavior of the isolator is required. Two of the authors of this research proposed a simplified hysteresis behavior of rubber to be used in FE model by mixing elastoplastic concepts and hyperelastic properties \cite{milani2011stretch}. In the present paper, a similar procedure is adopted. First, we generate a nonlinear behavior through a 3D FE simulation, based only on the hyperelasticity of the rubber pad, i.e., without different loading-unloading paths, see Figure \ref{249858}b. The dashed line represents the shear behavior obtained by the FE analysis of a UFREI-200. This displacement-force data is then inputted as the properties of a nonlinear spring at a structural level.