A new bi-linear constitutive shear relationship for Unbonded Fiber-Reinforced Elastomeric Isolators (U-FREIs)

Unbonded Fiber-Reinforced Elastomeric Isolators (U-FREIs) are valuable devices that can be used for seismic isolation of buildings. U-FREIs are cheaper than Steel Reinforced Elastomeric Isolators (SREIs), due to the U-FREI's light weight, ease of installation, and elimination of the need for steel end plates for anchoring to the structure. Moreover, good isolating properties of U-FREIs are demonstrated by a substantial number of publications available in the literature. A model to define a bi-linear constitutive shear relationship for U-FREIs on the basis of given experimental loading cycles is proposed in the paper. The relationship serves to simulate the isolator behavior for use in structural analysis software programs for the design of isolated buildings. The procedure to derive the relationship, provided by the model, is simple to implement. A comparison between results of shear tests and the relationship obtained from the proposed model and from previously existing models is performed. The comparison shows that, among the models considered, the proposed new model provides the most adequate relationship for the description of U-FREIs shear behavior.