Influence of Negative Stiffness Damper on Stay Cable with Neoprene Rubber Bushings

Stay cables on cable-stayed bridges are inherently low-damped flexible structural members. In order to improve their energy-dissipating capacities, external dampers are installed to control undesired cable vibrations. Typically, external dampers are mounted near the cable anchorage and their performance reduced in the case of longer cables. In addition to this, damper performance is also reduced by the presence of neoprene rubber bushings, which are provided to reduce the bending stresses due to live loadings. In this study, a concept of negative stiffness in an external damper is suggested to improve the damping of stay cables equipped with rubber bushings. An analytical approach is used to explore the modal behavior of a cable-damper system mounted with neoprene rubber bushings. The solution is expressed in the approximate (asymptotic approach) as well as the exact approach. An expression for effective damper location and design damping curves are proposed for the benefit of designers and researchers. The lower-bound limit of a negative-stiffness damper is also derived, and its effect on damper performance is explored. Damping contour plots are developed to select the required level of damping from the available system parameters.