A procedure for the direct determination of the required supplemental damping for the seismic retrofit with viscous dampers

This paper describes a simplified procedure to calculate the supplemental damping ratio that must be provided in order to rehabilitate existing buildings with viscous dampers. The proposed method has been developed according to both analytical and graphical approaches. The graphical formulation is based on the construction of constant design acceleration or constant design displacement curves. These curves allow to estimate the required effective damping as a function of the effective period, associated to the secant stiffness at maximum displacement. Combining these curves with constant ductility curves, which provide a correlation between the effective damping and the supplemental damping for given available ductility and damper typology, it is possible to determine the required supplemental damping and to design the damping system. The proposed method has then been verified through nonlinear dynamic analyses considering a set of RC plane frames. Finally it has been applied to a case study regarding an existing building located in Italy and designed without considering the earthquake action.