Design criteria for added dampers and supporting braces

The papers deals with the use of dissipative braces as retrofit solutions for existing moment resisting frame buildings.Braces are widely used in order to enhance performances of existing buildings under seismic loads, by adding stiffness and strength against inertial forces induced by earthquake ground motions.The braces can be equipped with supplemental dissipators in order to increase the overall energy dissipation capacity of the system and reduce stresses in the existing structures.In the present work, general design criteria for dampers and supporting braces are given and a simple design procedure based on the actual mechanical interaction between dampers and braces has been carried out.A number of design procedures have been proposed for dissipative bracing systems in frame structures.The procedures are often based on simplifying assumptions, due to the complexity of mechanical behavior of systems equipped with dissipative braces.Those assumptions make the procedures easier to use, but at the same time, less reliable in predicting the behavior of complex structures.In the present work, results are obtained without using two of the most common simplifying assumptions that neglect interaction between frame and braces: the use of the floor stiffness in order to characterize the frame behavior, and the use of equivalent systems with a single degree of freedom.The proposed design procedure has been tested on a moment resisting frame building and appears feasible for implementation on real structures.