Shaking table test of a steel frame structure with layered three-dimensional isolation

A three-dimensional (3D) base isolation system can enhance the seismic performance of steel frame structures. However, the notable coupling effects and rocking behavior in the superstructure will complicate the design of base isolators and weaken the seismic resilience of the 3D base isolation system. To realize the 3D isolation function and constrain the coupling effects and rocking behavior of steel frame structures simultaneously, a layered 3D isolation system is proposed through the combination of a horizontal base isolation with friction pendulum bearings and a vertical floor isolation with steel coil springs installed beneath the floor slabs. A series of full-scale shaking table tests of a two-storey steel frame structure were conducted to verify the effectiveness of the proposed system. The test results indicate that the layered 3D isolation system with flexible horizontal displacement constraint devices decoupled the horizontal and vertical motions of the superstructure and improved the seismic behavior of steel frame structures. The horizontal–rocking coupling effects of the superstructure typically associated with traditional 3D base isolation were significantly suppressed. Due to the vertical acceleration isolation effects, the layered 3D isolation system led to stabler normal pressures on the friction pendulum and lower friction forces compared to the horizontal base isolation system, which mitigated the horizontal–vertical coupling effects of the structure and the stick-slip motions of friction pendulums to result in higher horizontal acceleration isolation effects and self-centering capacities. The unfavorable influence of elevating the floor slab on the seismic behavior of the superstructure was compensated by the horizontal isolation at the base.