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Apparent weakening is the softening of a structure's apparent stiffness by adding negative stiffness to the overall system, which has the benefit of reducing the peak accelerations and base shears induced in the structure due to a seismic event. Apparent weakening is an elastic effect that does not reduce the main structural strength. To attain this behavior, negative stiffness can be introduced through the integration of negative stiffness devices. This study presents a novel smooth negative stiffness device (SNSD) consisting of cables, pulleys, and tension springs. A nonlinear mathematical model of the force-deflection behavior of the SNSD was developed and used to determine the optimal geometry for such a device. A prototype device was designed and fabricated for installation in a bench-scale experimental structure, which was characterized through static and dynamic tests. This paper also presents a numerical study on two other device configurations designed to achieve different force-deflection relations for use in an inelastic model building subject to a suite of historic and synthetic ground motions. In both the experimental prototype and the numerical study, the SNSDs successfully produced apparent weakening, effectively reducing accelerations and base shears of the structures. [ABSTRACT FROM AUTHOR]