An abaqus user element for the structural implementation of low-cost rubber seismic isolators in masonry buildings

Due to the need for seismic protection in developing countries, some investigations on low-cost seismic isolators have been performed. One of them is an unbonded 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 potency of world-wide application of 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, rotations, and torsion. The results show that the UEL model can reasonably fit the finite element model of a referenced UFREI. The proposed UEL model is helpful in 3D analyses of isolated structures using UFREIs.