Simplified Direct Assessment Method for Nonlinear Structures Equipped with Nonlinear Viscous Dampers

The insertion of fluid viscous dampers in building structures is an innovative technology which can improve significantly the seismic response. These devices could be very useful also in the retrofit of existing buildings. In this paper a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio which depends on the maximum displacement of the structure, so that iterative procedures are required. The method proposed in this study is composed by two steps. The first one requires the direct estimate of the supplemental damping ratio under elastic conditions. The second step extends the procedure to structures with nonlinear behaviour. Both graphical and analytical approaches have been developed. Finally, the simplified method has been verified through several applications and comparisons with nonlinear dynamic analyses.