Superelastic semi-active damping of a base-isolated structure

Abstract

A hybrid base isolation system that is composed of linear elastomeric bearings (EB), friction-pendulum bearings (FPB), shape memory alloy (SMA) wires, and magnetorheological (MR) dampers is proposed for the mitigation of seismic motions. Each subcomponent of the isolation system is employed for a unique task in managing superstructure response when ground motions are experienced. EB are provided to couple the superstructure and substructure in the vertical direction while partially decoupling the superstructure from lateral ground motion. FPB provide support for gravity loads and a restoring force when base drifts become large. SMA wires supply recoverable hysteretic behavior and serve as an additional restoring force. Finally, MR dampers provide variable viscous damping that can be altered in real time for intelligent amelioration of superstructure response. Neuro-fuzzy techniques are incorporated to model SMA and MR elements. A fuzzy logic controller is generated using a multi-objective genetic algorithm for optimal modulation of MR damper resistance levels. To evaluate performance of the proposed isolation system the Phase II, Part IV Base Isolation Benchmark Problem is adopted and standard performance metrics are considered. The nominal isolation system of the problem statement is augmented with SMA and MR devices. Hysteretic behavior of each device is analyzed and their complimentary behavior is identified. Results of several control cases are provided that include semi-active and passive operation of the MR dampers and several configurations of SMA wires. Results show that the proposed superelastic semi-active base isolation system can reduce base drifts by 18% and maintain favorable superstructure response. Copyright © 2008 John Wiley & Sons, Ltd.