The main purpose of this research is to investigate the effects of different vertical distributions of the properties of nonlinear fluid-viscous dampers for the retrofit of existing multi-story reinforced concrete frames. In particular, the different distributions are defined on the basis of the same value of the supplemental damping ratio. Since the viscous dampers are used for the retrofit of existing buildings, they are dimensioned assuming that the structure can exceed the elastic limit, with the only condition to satisfy the prefixed performance limit. In the design phase the different vertical distributions of damper properties are compared in terms of the total sum of the damping coefficients. The effectiveness of the different distributions is then examined by performing time-history analysis of several case studies considering a nonlinear behavior both for the viscous dampers and for the structural members. The results of the nonlinear dynamic analyses are examined in terms of inter-story drifts and dampers forces. The considered case studies are five RC frames characterized by different number of stories (3, 6 and 9 stories) and also by different properties in terms of regularity in elevation. In this way it is also possible to investigate the effect of the vertical distribution of the damper properties for regular and irregular frames.
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