Seismic response mitigation in fixed-base inelastic structures using negative stiffness device (NSD)

Underlying Principle

Yielding can be emulated in a structural system by adding an adaptive "negative stiffness device" (NSD) and shifting the "yielding" away from the main structural system-leading to the new idea of "apparent weakening" that occurs ensuring structural stability at all displacement amplitudes. This is achieved through an adaptive negative stiffness system (ANSS), a combination of NSD and a viscous damper. By engaging the NSD at an appropriate displacement (apparent yield displacement that is well below the actual yield displacement of the structural system) the composite structure-device assembly behaves like a yielding structure. The combined NSD-structure system presented in this study has a re-centering mechanism thereby avoids permanent deformation in the composite structure-device assembly unless, the main structure itself yields. Essentially, a yielding-structure is "mimicked" without any, or with minimal permanent deformation or yielding in the main structure. As a result, the main structural system suffers less accelerations, less displacements and less base shear, while the ANSS "absorbs" them.

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Objective

In the second phase of this study, the concept of "weakening and damping" is verified in a prototype 1:3 scale moment-frame designed at University at Buffalo (UB) and tested by the researchers at UB and Rice Univeristy. The objective of this study is to verify the performance of NSD, built by Taylor Devices, Inc., in yielding structures. The test frame is subjected to set of peer ground motions resulting in the yielding of columns in the first story. By adding the negative stiffness device the structure experiences lower accelerations and base shear, while the increased deformations are controlled and reduced by viscous-fluid supplemental dampers.

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