Direct assessment of the nonlinear seismic response of RC frames with viscous dampers

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 provides the direct estimate of the supplemental damping ratio under elastic conditions. The second step extends the procedure to structures with nonlinear behaviour. The direct method has then been applied to a set of different RC frames. Its effectiveness has been studied through comparisons with several nonlinear dynamic analyses. Moreover, an investigation has been performed with regard to the influence of the relations that define the damping reduction factor and the hysteretic damping.