Seismic protection of base-isolated structures using semi-active MR dampers

Magnetorheological (MR) damper is one semi-active device that shows a great potential for vibration suppression and hazard mitigation of civil structures. One special advantage of the damper is that its damping characteristics can be adaptively and quickly altered by a varying magnetic field. This semi-active damper has been shown to be more effective than passive dampers in reducing the seismic response of flexible structures with a dominant natural period of 1.5 see or more. Examples of these structures include base-isolated structures, cables of long-span bridges and tall buildings. In this study, the effectiveness of MR dampers for seismic protection of base-isolated structures is investigated. The damper is commanded by an inverse Bouc-Wen model together with a linear quadratic regulator (LQR) algorithm. An elevated highway bridge, modeled as a 2-degree-of-freedom system, is used to illustrate the effectiveness of the MR damper in protecting a base-isolated structure.