FINITE ELEMENT ANALYSIS OF HIGH DAMPING UNBONDED FIBER REINFORCED ELASTOMERIC ISOLATORS (UFREIS) OF DIFFERENT SHAPE FACTORS

Losses and damages induced by earthquakes are a dramatic reality worldwide. Consequently, implementing innovative protection strategies for existing and new constructions is of societal importance. Elastomeric isolators are special devices for the seismic isolation of structures. Typically, they are made of layers of steel laminas and rubber, and they are interposed between the ground and the structure to increase the natural period and reduce the inertia forces to apply in case of an earthquake. Fiber-reinforced elastomeric isolator (FREI) is a new type of elastomeric isolator. Instead of steel laminas, thin fiber layers are used for vertical reinforcement. Compared with the steel-reinforced ones, FREIs have considerably lower weight and can be manufactured through cold vulcanization. They can be applied to the structure in several methods: bonded, unbonded, partially bonded, and friction (no bonding between rubber and fiber layers). In unbonded applications (UFREI), the isolators can simply be installed between the upper structure and foundation without bonding or fastening. So, the shear load is transferred through the friction generated between the UFREI and the structure surfaces, improving the dissipation energy of the device. This study proposes a detailed 3D finite element modeling of UFREIs, considering different shape factors. The devices, made of high-damping rubber and glass fiber-reinforced polymer laminas, have been subjected to a cyclic horizontal displacement up to 150% of the total height of the rubber pads under constant vertical pressure. Results evaluated in terms of horizontal stiffness, damping ratio, and horizontal period have highlighted the significant influence of the shape factors on the final lateral response of the UFREIs.