Implementation and validation of a simple abaqus user element for unbonded fiber reinforced elastomeric isolators (UFREIs) in masonry housing protection

The seismic protection of masonry housing in developing countries is of key societal importance. Consistently with this need, some investigations on low-cost seismic isolators have been performed. One of them is an un-bonded fiber reinforced elastomeric isolator (UFREI), in which the bearing is not bonded to the supports. This type allows the application of base isolation without any expensive thick-steel plate for supports. The UFREI is considerably effective for utilization on low-rise buildings, even masonry housings. Advantageous features of the UFREI are the roll-over and full-contact deformations. The former can decrease the effective stiffness of the isolation system, lowering the seismic force demand. Meanwhile, the latter plays a role in generating a hardening effect, limiting the shear displacement of the base isolation under a maximum earthquake. Those remarkable advantages reveal a great potential of world-wide application for UFREIs. However, there is no representative model of UFREI in the various software of structural analyses. In this work, a comprehensive but simple model of UFREI is implemented in an ABAQUS user element (UEL), taking into account the softening, hardening, and hysteresis effects of the bearing. In addition, multiple DOFs are considered to characterize the complex 3D behavior of a UFREI in lateral, axial, flexural, and torsional dofs. A validation is performed by isolating a rigid slab (e.g. the foundation slab of a masonry house) using four different isolators to produce torsion and rotation during seismic motion. The results show that the UEL model can reasonably fit the behavior of UFREIs, with a significant reduction of computational efforts. The proposed UEL model is particularly helpful in 3D dynamic analyses of isolated structures using UFREIs.