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Recent earthquakes have highlighted the high seismic vulnerability of the structures and the need of retrofitting interventions. Different seismic protection strategies and techniques can be used to increase the seismic capacity of existing masonry constructions. Common retrofitting techniques are generally based on a strengthening approach. Instead, innovative retrofitting strategies can be used to mitigate the effect of earthquakes, with the aim of decreasing the seismic demand on the structure or increasing its energy dissipation capacity. One of the most innovative devices is the Unbonded Fiber Reinforced Elstomeric Isoletors. UFREIs are made of alternate layers of fiber and rubber and they are interposed between the ground and the foundation, with the particularity that no bonding or fastening is provided between the bearing and top-bottom supports. In this paper, through the FE software code Abaqus, a series of nonlinear dynamic analysis are performed to investigate the influence of crosslinking on the seismic performance of UFREI made of regenerated rubber. Numerical results show that the devices vulcanized at 130°C for 40 minutes, although having suboptimal crosslinking density, are suitable to properly isolate low-rise buildings.

Losses and damages induced by strong earthquakes are a dramatic reality worldwide. As a consequence, the implementation of innovative protection strategies for both existing and new constructions is of key societal importance. Elastomeric isolators are special devices for seismic isolation of structures. Typically, they are made of alternate layers of steel or fiber reinforced laminas and rubber and they are interposed between the ground and the foundation in order to increase the natural period of the structure and reduce the inertia forces to apply in case of an earthquake. This study proposes a detailed 3D FE modelling of isolators conceived for low-rise masonry buildings in developing countries, carried out through the FE software code Abaqus. The isolator under study consists of an energy dissipation core made by relatively High Damping Rubber and an external EPDM ring. In addition, in order to reduce the production cost and allow its applicability in developing countries, it presents unbonded boundary conditions. In fact, the upper and lower edges do not exhibit any bond with the supports. The main feature of such a device is the large deformability thanks to the rollover deformation and the favorably lower lateral stiffness compared to the bonded isolator.