Strengthening of Vulnerable RC Moment Resisting Frames Using Direct Internal Connection of X-Steel Bracing

Abstract

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