Seismic Protection of R/C Structures by a New Dissipative Bracing System

This study presents the results of numerical investigations carried out on a new alternative dissipative bracing system for improving the seismic performance of R/C frames. The proposed system is composed of ductile shear panel and concentric X-braces, and can be used to provide both ductility and stiffness to existing structures. Under seismic actions the braces are expected to remain elastic, while the panel dissipates significant amount of energy by yielding. A simplified model of the bracing system is developed for global analyses of frames. An energy based design procedure for seismic upgrading of frames with ductile shear panel and concentric X-braces is presented. This simplified procedure, based on energy balance concept and nonlinear static analyses, can represent an advantageous approach in preliminary analysis and design stage. Results of nonlinear dynamic analyses performed on a four-story R/C frame designed only for gravity loads show that the proposed bracing system can protect the primary structural elements of the frame preventing them from damage under severe seismic actions.