Seismic protection of SDOF systems with a negative stiffness amplifying damper

A new passive device named negative stiffness amplifying damper (NSAD) is proposed in this paper by introducing a negative stiffness (NS) spring into to the flexibly-supported-viscous-damper systems (represented by classical Maxwell damping element, MDE).. The NS spring is combined with the dashpot of the MDE, amplifying the stroke of the dashpot; therefore, lead to significant damping magnification effect. The proposed NSAD not only achieves significant damping magnification effect, but also preserves the property of negative stiffness. This feature is attractive for reducing both displacement and structural acceleration when subjected to earthquakes. The closed-form expressions of optimal parameters for an undamped SDOF system with a NSAD is also proposed by modifying the 'fixed point' method of tuned mass damper. Then, the performance of NSAD is investigated and evaluated under stochastic excitations, pulse excitations, and real earthquakes. Result shows that the optimal NSAD can substantially reduce displacement and acceleration responses simultaneously. For instance, even using the same small additional damping ratio (i.e., 2.8%), the optimal NSAD reduces the resonance response of MDE by 76.9%. Also with that small additional damping, the NSAD improves the energy dissipation capability by 5-16 times, causing 40-60% of seismic response reduction for most structural period range. Moreover, the NSAD is also effective for both far-field and near-fault earthquakes. Especially for near-fault pulse-like earthquakes which may potentially cause larger seismic responses for long-period structures, the NSAD provides an extra improvement of 15-20% in energy dissipation capability for long-period structures.