Strengthening of vulnerable RC moment resisting frames using direct internal connection of X-steel bracing

Non-ductile reinforced concrete frames are commonly found in older buildings many parts of the world. These structures designed for gravity loads, have limited lateral strength and ductility, prone to excessive one-way movement soft-story mechanism. This paper focuses on retrofit an existing frame, using steel X-braces by direct internal connection method. The main purpose is analytical study general behavior response large scale vulnerable frames. An experimental was used validate numerical modeling performed ABAQUS. Next base samples were retrofitted with four proposed methods. Furthermore, a separate parametric studies, effect frame type, bracing cross-section dimensions gusset plate shape investigated. results indicated that stiffness, bearing capacity absorbed energy increases up 4, 2.3 1.5 times, respectively. Moreover, acts like first defense system against such as structural fuse its yield, amount dissipation. It also removes plastic hinges reducing ultimate displacement stress load panel zone.