Introduction and Performance Investigation of a Hybrid Base Isolation System with Re-centering Capability

Regarding the high cost of retrofitting and replacing the isolation system after an earthquake, re-centering seismic isolation systems have become one of the most popular research fields in the past decades. A new generation of seismic isolation is based on equipment with improved performance in terms of damping and re-centering capability. Since lead-rubber base isolation (LRB) is one of the most common seismic isolation systems, this paper focused on suggesting a re-centering LRB system with high damping capacity. The LRB isolation is based on an experimental study under a constant vertical load equal to 650 kN. The proposed combined system of LRB and friction yields a high damping capacity. A spherical shell is placed on the base isolation system, and the friction reaction emanates from this shell's sliding on the provided foundation. The primary purpose of this spherical shell is to increase the damping capacity of the isolation system. An adjustable friction reaction is reachable depending on the connection details of the spherical steel shell with the system's upper steel cap plate. The higher stiffness of this connection is provided greater friction force and, as a result, higher damping capacity. In short, this connection was performed as adjustable friction and can increase energy dissipation and maximum shear force, respectively, in the range of 12% to 80% and 6% to 230%. Increasing re-centering capacity is another goal of this study. It is of great interest to implement shape memory alloy (SMA) in the form of wires because of their re-centering capabilities. The axisymmetric design is implemented to reduce this hybrid system's vulnerability to earthquakes of arbitrary direction. The combined action of wires and the spherical steel shell provides the re-centering capacity of the system.The final system, which is a combination of LRB, friction mechanism, and vertical load transfer through SMA wires (MDLRB-SMA), exhibits enhanced properties such as reduced residual deformation, controllable shear reaction at each stage of the deformation, and increased damping capacity. The energy dissipation capacity of the MDLRB-SMA is shown to be increased by 50%, with a decreased residual deformation of up to 45% compared to the LRB. A set of parametric studies are also performed to investigate the influence of frequency, displacement amplitude, loading rate, the wires' configuration and properties, and the aspect ratio of the system's performance.