FVDs AND HYSTERETIC STRUCTURES: DESIGN STRATEGIES

Nowadays fluid viscous dampers (FVDs) are among the most used passive energy dissipation devices thanks to their capacity to generate velocity dependent dissipative forces, not in phase with the displacements, that exhibit their maximum value when internal restoring forces are minimum. Often preferred over other types of dampers, FVDs have also the advantage of increasing the damping ratio of structures without significantly altering the inherent stiffness. One of the issues, mostly connected to the structures exhibiting a nonlinear plastic behavior, despite the structures maintaining an elastic one, is the absence of specific code prescriptions and simple, but sufficiently reliable, design strategies. To overcome this lack could make the use of viscous dampers, characterized by a linear or, more generally, nonlinear velocity dependence of the dissipative forces, more diffused than it is. With the aim of simplifying the procedure for practical applications, a novel design strategy for nonlinear FVDs to apply to hysteretic reinforced concrete framed structures is proposed and discussed in terms of reliability, by analyzing the results in a statistical sense. An initial hypothesis, consisting of a simplified dynamic structural response assumed to be coupled to the equivalent linearization of FVDs, is necessary for this scope. To prove the suitability of this hypothesis, a comparison between the obtainable results and the design targets is carried out for those structures that do not satisfy the assumed hypothesis, through time history analyses performed on FVDs-equipped (and non) structural nonlinear models. Benchmark models, subjected to appropriate families of base accelerograms, are analyzed to test the procedure and its degree of success in connection to the assumed target objectives.