Simulated Bilinear-Elastic Behavior in a SDOF Elastic Structure Using Negative Stiffness Device: Experimental and Analytical Study

The acceleration and base shear of structures during strong ground motion can be attenuated by achieving bilinear-elastic behavior without any permanent displacement—also referred to as "apparent weakening." The negative stiffness device (NSD), used in this study, exhibits nonlinear-elastic negative stiffness behavior; by adding NSD to the elastic structure, the resulting structure-device assembly behaves like a bilinear-elastic structure. Peak acceleration and base shear experienced by the structures can be reduced by adding the negative stiffness device, and the additional deformations caused by the reduced stiffness can be contained by adding a viscous damper. This paper presents the experimental study on a three-story fixed-base structure (3SFS), acting as a single-degree-of-freedom (SDOF) system (because of bracing in the top two stories), that demonstrates the concept of apparent weakening in elastic structural systems. Two NSDs and a viscous damper are installed in the first story of 3SFS. To accentuate the advantages of incorporating NSD in structures, responses of four different systems—3SFS, 3SFS with damper, 3SFS with NSD, and 3SFS with NSD and damper—are compared for a suite of ground motions. The behavior of all the three systems is also predicted analytically, and the predicted results are in excellent agreement with the experiments. Shake-table tests on 3SFS have confirmed that by adding the NSD and damper, acceleration and base shear of the structure are reduced by more than 30% and the displacement of the structure is reduced by more than 20%.