Adding stiffener to Circular Hollow Section CHS connection is a common method to strength this type of connection. This manuscript investigated the effectiveness of using stiffener with CHS T-joint subjected to cyclic load. Four full scale specimens were experimentally studied under cyclic load, two specimens were unreinforced joints, and the others were reinforced with stiffener. Hysteretic curves were plotted from load displacement data and S curves were extracted from them. The failure mode, the hysteretic curves and energy dissipation of the four full-scale specimens were examined, and it was found that the integrated area within hysteretic curves of the stiffened T-joints is larger than the enclosed area of the un-stiffened specimens because chord reinforcement improved the joint bearing capacity. Finite element (FE) analysis was conducted using the ABAQUS soft package. Results obtained from Finite element models (FEM) were verified with experimental results and found in favorable agreement with experiment results. Stress distribution displayed from FEM and compared with fracture observed from experiments. FEM is extended to study the effect of external stiffeners on CHS T-Joints’ capacity with different brace to chord diameter ratios β. Although external stiffeners decreased stress concentration around joints by increasing load distribution area, positive joint capacity enhanced by 10% and there was an unremarkable improvement in a negative capacity. By the end of the research, the imperial formulation for joint capacity was performed and examined by the experimental and numerical results.