Bonded versus unbonded strip fiber reinforced elastomeric isolators: Finite element analysis

This paper presents a finite element (FE) model for the analysis of strip fiber reinforced elastomeric isolators (FREIs) that are subjected to any given combination of static vertical and lateral loads. The model is able to simulate both bonded and unbonded boundary conditions at the top and bottom contact surfaces of the isolator. Compared to bonded (B)-FREIs, the FE-analysis of stable unbonded (SU)-FREIs presents additional analysis challenges. SU-FREI refers to unbonded FREIs that exhibit stable rollover deformation under lateral loads. Additional analysis challenges are attributed to changes in the boundary conditions of SU-FREI as a result of rollover type deformation. To address these challenges, the utilized FE-mesh is updated during analysis consistent with the deformed geometry of the isolator. Using the proposed FE-model, the lateral responses of a B-FREI and a SU-FREI were evaluated. Both isolators had the same material and geometrical properties and were subjected to identical constant vertical loading. Comparing the lateral responses, it was found that the SU-FREI was considerably more efficient than the B-FREI as a seismic isolator. In addition, the in-service stress demands on the SU-FREI were found to be significantly lower than the B-FREI.