In recent years, it has been recognized that Negative Stiffness Devices (NSD) may be suitable for seismic protection of structures. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (i.e., the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an "apparent weakening and softening" of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non-damaging nature in that it occurs in the NSD's rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the adaptive stiffness device. The combination of adaptive negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically-isolated bridge model that is subjected to various strong earthquake ground motions. The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. The seismic performance of the bridge model is being investigated as part of the NEES-ADAPT Project which includes shaking table tests of the bridge to validate the results from the numerical simulations.
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