Experimental investigation of joint shear deformation in real-scale RC beam–column joints with different reinforcement layouts under cyclic loading

The deformation response of reinforced concrete (RC) beam–column joints is strongly influenced by the internal reinforcement layout of both the joint core and the adjoining beam. Further, since the joint region is shear-critical in performance, the size effects in both the concrete member geometry and reinforcement detailing need special attention. This study experimentally investigates the evolution of joint shear deformation in full-scale (real-size) exterior reinforced concrete beam–column joints with different reinforcement layouts subjected to quasi-static cyclic loading. Full-scale specimens were tested under constant axial load and increasing lateral drift demands, allowing a direct assessment of joint deformation mechanisms up to moderate-to-high drift levels. The experimental programme included reference specimens without joint reinforcement, specimens incorporating different reinforcement layouts, and joints strengthened with externally bonded X-shaped carbon fiber-reinforced polymer (C-FRP) ropes. Joint behaviour was evaluated through direct measurements of diagonal deformations, from which average joint shear deformation and normalized joint shear stress were determined. The results show that the reinforcement layout significantly influences the deformation capacity and damage evolution of the joint. Reinforced specimens exhibited lower joint shear deformation, improved control of shear-induced damage, and a more stable response under increasing cyclic drift demands compared with the reference specimens. Among the investigated configurations, the combined use of internal reinforcement detailing and X-shaped C-FRP rope strengthening provided the most effective overall performance by reducing joint deformation and delaying damage progression. The experimental findings provide a systematic comparison of different reinforcement layouts and contribute to a better understanding of the relationship between joint shear deformation, normalized joint shear stress, and damage evolution in exterior RC beam–column joints subjected to cyclic loading.