A Methodology for the Direct Assessment of the Damping Ratio of Structures Equipped with Nonlinear Viscous Dampers

The expressions proposed in literature for the supplemental damping ratio provided by nonlinear viscous dampers usually include a term related to the structural response, so that iterative procedures are required. This article proposes a simplified method for the direct assessment of the supplemental damping ratio on the basis of a new dimensionless parameter, called damper index. The methodology has been verified through numerical investigations, considering single- and multi-degree of freedom systems subjected to harmonic excitations and ground motions. A procedure is also proposed for obtaining design spectra of the damping ratio in terms of the damper index.