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Seismic Control of Civil Structures Utilizing Semi–Active MR Braces

This paper presents the feasibility and effectiveness of magnetorheological (MR) braces in earthquake hazard mitigation. In doing so, a nondimensional variable, β, which is the ratio of the yield force of the MR damper to forcing input (the product of a characteristic mass of the building and the seismic acceleration) is used to design the MR damper preventing the locked damper motion that may worsen seismic response of the building. From this theoretical analysis, the activation gap of the damper as an important design parameter to prevent the locked damper motion is chosen. Based on this analysis, the MR damper is fabricated by modifying the commercial MR damper of Lord Corporation, SD–1000–1. Then, a three–story building with MR braces is constructed and its dynamic equation is theoretically derived. In order to investigate semi–active control methods to MR braces, three different control algorithms are formulated and evaluated both numerically and experimentally. The results show that control of the building with semi–actively controlled MR braces is very effective.