Evaluation and Comparison of Divergent and Convergent Bracing Performance in Strengthening of Reinforced Concrete Frames

The steel bracing system is one of the appropriate methods for the strengthening of concrete moment frames against lateral forces. The article purpose is the evaluation of the new strengthening method of reinforced concrete moment frame with convergent bracing and interchangeable link beams that is embedded in the steel frame and installed in the concrete frame spans. This new method is easy to execute, economical and ductile with appropriate performance because of the existence of ductile fuse in its accession section. Therefore, this method is introduced and compared to other strengthening methods by steel bracing. In this article six concrete frame strengthening methods investigated include x-convergent bracing, reverse chevron bracing, divergent bracing with concrete link beam, divergent bracing with steel link beam connected to steel columns in the steel frame, divergent bracing with steel link beam connected to the steel frame with steel columns between those two, divergent bracing with steel link beam connected to the steel frame. All strengthening models attached to concrete frames by a steel frame surrounding them. The linear dynamic analysis results showed a decrease in relative lateral displacement and stress ratio of concrete frame members in all strengthed frames compared to the nonstrengthed frame. Also in the strengthed frame by divergent bracing and steel link beam, the results revealed a 38% steel consumption decrease and an 18% base shear decrease compared to strengthed frame by x-convergent bracing. Nonlinear static and dynamic analysis of models were done by PERFORM-3D software. The nonlinear behavior results of the strengthed concrete frame by divergent bracing with steel link beam connected to the steel frame showed more stiffness, ductility, behavior coefficient and energy dissipation than other models. Also, in this model, an appropriate performance of the structural fuse was shown by the plastic hinge formation of the link beam.