Seismic Performance of SDOF System with a Negative Stiffness-Inerter System

The seismic mitigation performance of the negative stiffness-inerter system (NSIS) is investigated by frequency-domain analysis and time-history analysis. In the NSIS, the inerter is connected with a dashpot and a negative stiffness (NS) spring in parallel, which amplifies the stroke of the dashpot. Therefore, the inerter and the NS provide a significant damping magnification effect, and this feature is desired for reducing the structural responses effectively when subjected to earthquakes. The closed-form expressions of optimal parameters for an uncontrolled SDOF system with NSIS are proposed by the “fixed point” method. Then, the performance of NSIS is evaluated under actual earthquakes. Results show that the optimal NSIS can substantially reduce the displacement and acceleration responses of the SDOF system simultaneously under far-field earthquakes. For instance, the seismic responses for most structural period ranges can be reduced by 20%–55%. Besides, the seismic mitigation capacity of the inerter system (IS), the negative stiffness amplifying damper (NSAD), and the NSIS are compared, and these three systems utilize the optimal parameters. The results show that when the structural period is smaller than one sec, the displacement responses of NSIS are 20% less than the IS and 11.1% less than the NSAD. And, the acceleration reduction ability of the NSIS is better than the IS but worse than the NSAD.