Effective numerical modeling of unbonded rubber isolation for masonry housing

Another important issue is the modelling of UFREIs in structural analysis. The non-linearity model of this isolator, including the softening and hardening, is not found in the most structural analyses software available \cite{simulia2013abaqus,csi20108}. Some works implemented a numerical model of UFREIs only up to the softening mode \cite{das2016comparison,manzoori2017application}. The hardening branch was usually excluded because it was considered as the unstable part.
 
First of all, a detailed 3D model of a single isolator is implemented into ABAQUS and its hysteretic behavior is numerically analyzed. A preliminary validation is provided assuming as reference some existing experimental data obtained on a standard UFREI subjected to hysteretic cycles. The proposed UFREI is then identified with a single DOF system constituted by a spring exhibiting softening during a cycle, this latter is quite low and can be disregarded without meaningful errors for structural applications. The identification of the 3D model behavior with a single DOF system (non-linear spring with damping) is mandatory to perform large scale non-linear dynamic analyses on isolated full scale buildings. 

Numerical model of fiber reinforced elastomeric isolator