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Negative stiffness systems have shown promising performance for low-frequency vibration isolation by reducing structure stiffness. However, this approach is still a passive vibration control strategy with a limited control frequency range. Magnetorheological fluid (MRF) and related adjustable devices hold the potential to resolve this issue. In this paper, we present a novel system that parallels a three-spring mechanism and a magnetorheological (MR) damper to enable adjustable negative stiffness vibration isolation. The three-spring mechanism combines springs, cams, and rollers to exhibit negative stiffness, while the MR damper provides adjustable damping force when a varying current is applied. The resulting force-displacement hysteresis curve of the paralleled system demonstrates adjustable stiffness and damping simultaneously. This paper firstly presents the theoretical analysis of the three-spring mechanism to obtain the optimum configuration of the stiffnesses of the springs. The MR damper is then designed and analyzed. Subsequently, the parallel system is manufactured and tested under harmonic excitations with considering different frequencies and amplitudes. The corresponding mechanical model is then formulated according to experimental results. Lastly, the vibration isolation performance of the proposed system is validated through comparative numerical studies based on a three-story building model, considering different control strategies and earthquake inputs.
 

Negative stiffness,Magnetorheological damper,Vibration control,Semi-active control,Seismic protection