Seismic Performance of Steel Frame Structures with Layered Three-Dimensional Isolation System

There is a need to improve the vertical behavior of steel frame structures to enhance their seismic resilience during strong earthquake events. A three-dimensional (3D) base isolation system with 3D isolators installed at the base of the structure can further improve the seismic performance of steel frame structures compared to horizontal base isolation. However, significant 3D motion coupling and rocking behavior of the superstructure because of its high gravity center will cause a complex design of the isolators and weaken the seismic performance of the structural and nonstructural components. To realize the 3D isolation function and constrain the motion coupling and rocking behavior of steel frame structures, a layered 3D isolation system (L3DIS) is proposed. The horizontal isolators are installed at the base of the superstructure as in a traditional isolation system, and the vertical isolators are placed under the floors by separating them from the beams in the proposed system. The seismic responses and rocking constraint effects of the L3DIS are analyzed through a series of shaking table tests. Fixed-base and horizontally base-isolated systems are also considered in the experiment. The results show that the L3DIS can effectively mitigate the horizontal acceleration of the whole structure to protect the structural members and control the vertical acceleration of the floor slabs to protect the non-structural components. As the gravity center of the floor slabs is low, the motion coupling effects and rocking responses of the floor slabs can be significantly suppressed.