Variable Negative Stiffness Device for Seismic Protection of Building Structures through Apparent Weakening

In the present work, the variable negative stiffness device (VNSD) is presented for seismic protection through apparent weakening. Equations relating the force-displacement behavior for two different VNSD configurations are presented, and a parameter search is conducted to identify the system parameters leading to three different desired force-displacement profiles. Validation of the concept is provided through laboratory testing on a small-scale prototype subject to cyclic loading. Then, numerical simulations are performed for an inelastic building model with supplemental damping and three different VNSD systems subject to a suite of earthquake ground motions. The results show that the performance of the VNSD systems with and without stiffening was the same for the structure without yielding, and comparable when the structure experienced severe yielding. For the structure subject to extreme yielding, significantly larger peak displacements and smaller peak absolute accelerations and base shears were obtained for the VNSD system without stiffening. Finally, the effect of increasing supplemental damping in the structure on the performance of the VNSD systems was investigated.