Aseismic design of structure–equipment systems using variable frequency pendulum isolator

Abstract

Sliding isolation systems have emerged as very useful vibration control technique that incorporate isolation, energy dissipation and restoring mechanism in one unit. However, most currently available systems such as friction pendulum system (FPS) and pure friction (PF) system have practical limitations and are of limited effectiveness when input excitation level is significantly different from its design level. To overcome these limitations while preserving the advantages, a new system called the variable frequency pendulum isolator (VFPI) has been developed by the authors. The isolation period of VFPI continuously decreases with increase in horizontal sliding displacement which results in a more robust isolation system. The VFPI also limits the maximum force transmitted to the structure by providing a restoring force-softening mechanism. In this paper, it has been shown that isolating a structure using VFPI is very effective for vibration control of structure–equipment and other primary–secondary systems. An example five-storey structure with equipment mounted at its top has been analysed to demonstrate the effectiveness of VFPI. It is shown that VFPI provides better vibration control properties compared to other friction isolation systems, and excellent response reduction is observed for a wide range of equipment properties and excitation characteristics . The performance of the example structure with VFPI has been compared with the other frictional systems such as FPS and PF system.