Negative stiffness device for seismic protection of MDOF yielding fixed base structures: Experimental and analytical study

Shake table tests of single degree of freedom elastic/inelastic structures have confirmed that by adding a negative stiffness device (NSD), capable of exhibiting nonlinear elastic negative stiffness, in conjunction with a viscous damper, the acceleration, inter-story drifts, and base shear can be reduced significantly. However, little is known about how the presence of NSD/damper in the first story influences the response of higher stories of a multistory structure. In this paper, shake table test results are presented that demonstrate the advantages of NSD/damper in the first story of a multidegree of freedom, three-story, fixed-base structure (MDOF-3SFS). Results confirm that deployment of NSD/damper at the first story leads to significant reductions of acceleration as well as base shear and inter-story deformations in the MDOF-3SFS. Essentially, an NSD and a damper in the first floor prevents the transmission of the input energy from the ground motion to the second and third story of the multistory structure by deflecting and dissipating energy. If the first-story displacements become excessive, NSD stiffens and prevents collapse. The efficacy of the NSD/damper system is further demonstrated by comparing it with the performance of a structure with passive viscous dampers deployed in the first story. In addition to the reduction of base shear and maximum accelerations, the NSD/damper system also restricts large deformations to the first story only, leading to minimal damage to the whole structure. Finally, an NSD-based bracing system is introduced that can be deployed in new and existing structures.