Polynomial friction pendulum isolators (PFPIs) for building floor isolation: An experimental and theoretical study

Compared to structural base isolation, floor isolation is a more cost-effective and efficient means for seismic protection of vibration-sensitive equipment in a building structure. In this study, a multi-functional floor isolation system (FIS) that consists of several variable-stiffness sliding isolators, called polynomial friction pendulum isolators (PFPIs), is proposed and studied experimentally and numerically. Due to its variable-stiffness nature, the proposed PFPI-FIS is able to achieve multiple design objectives. This paper also demonstrates the procedure to design a prototype PFPI-FIS which meets the desired dual performance objectives for two-level seismic loads. The shaking table tests verify that the prototype system possesses the desired hysteretic property with variable stiffness, and the measured responses match very well with the simulated ones. Moreover, by considering ten ground motions that represent earthquakes with different spectral contents, the seismic responses of the prototype PFPI-FIS under these ground motions with different intensity level are simulated extensively. The simulated results demonstrate that the isolation performance of the PFPI-FIS does comply with the designated dual performance objectives, which yield either acceleration or displacement control depending on the earthquake intensity and isolator drift.