Experimental Evaluation of Multi-functional Nonlinear Floor Isolation Systems

Abstract

Acceleration-sensitive equipment housed inside of buildings is susceptible to damage from strong floor motions of the primary structure produced by earthquakes. Floor isolation systems (FISs) represent an effective strategy to protect such equipment from these motions by decoupling the equipment from the primary structure. However, even the most effective isolation systems are incapable of protecting equipment from building collapse in the event of strong ground shaking. This study experimentally explores the use of a novel multi-functional FIS capable of mitigating both equipment accelerations and facility drifts by passively adapting to achieve desired building-system performance. For low intensity disturbances, the system functions like a traditional isolation system, but for high intensity events, impacts in the isolation system act to increase the coupling between the primary structure and the FIS, pumping energy like a vibro-impact absorber. A scale experimental model, consisting of a three-story frame and an isolated mass, is used to demonstrate and evaluate the design methodology via shake table tests. The dynamic properties of the experimental model are identified, and the isolator’s displacement capacity and the disturbance frequency and amplitude provide the parametric variation. The performance of the multi-functional FIS was established and is described in this study.