Experimental and analytical investigation of a new three-dimensional seismic isolation under coupled horizontal-vertical excitations

This study investigates experimentally and analytically the performance of a new Three-Dimensional Seismic Isolator (3DSI) designed to control the horizontal-vertical coupled responses of multi-story buildings. The proposed isolator system adopts the concept of Super-High-Damping-Rubber (SHDR) to achieve vertical isolation by decreasing the vertical effective stiffness and increasing the vertical effective damping, thus minimizing the imparted vertical acceleration into the superstructure. Three different case-study buildings, including dual 5-story steel frames with Fixed Base, Conventional Seismic Isolators (CSI), and the proposed 3DSI, were analysed using OpenSees software based on experimentally validated models under a set of 12 earthquake records. The vertical period of the isolator system was tuned to reach 0.3 s, at which most of the vertical ground motions are degraded to less than 2.0 g. The results indicate that the proposed 3DSI system can considerably decrease the vertical and horizontal responses by up to 65% and 20%, respectively, compared to the CSI system. It is shown that using the 3DSI system minimizes the potential damage by reducing the magnitude of the vertical responses, while it also leads to smaller compression and tension axial loads and less inter-story drifts. In contrast, Fixed Base and CSI buildings experienced significantly escalated vertical accelerations, particularly on long-span beams, potentially leading to extensive non-structural damage during strong earthquake events.