Abstarct: Beam-column connections in reinforced concrete structures are one of the most important structural elements to realize moment frxame behavior. Many reinforced concrete joints in Iran have common seismic weaknesses, such as the absence of transverse reinforcement in the connection area or insufficient bond length of the beam bottom bars in the connection area. There are various approaches to retrofitting such joints, one of the most practical of which is the use of enlarging the connection area with steel angles. Researchers have provided a lot of experimental studies on beam–column connections, while experimental studies are usually costly and time consuming, and can be restricted by the test facilities. The finite element method is one of the methods used by many researchers to investigate parameters affecting the behavior of joints. But due to the complexity of the stress in the joint area and the effects such as continuity, concrete cracking is generally not feasible for the engineer to understand the desirable behavior of finite element analysis. The strut and tie method has been recognized as an acceptable tool in concrete Code for investigating the behavior of concrete members. considering the advantages of strut and ie method in this study, we are looking to develop strut and tie method towards nonlinear methods and to incorporate nonlinear effects in strut and tie model. For this purpose, after selecting the laboratory models and before entering the strut and tie models, a limited component effort was attempted for control samples with different seismic and non-seismic details and retrofitted specimens and tried to obtain parameters that mainly analytical research is ignored, such as the effects of bond slip, with a new approach recently introduced. After validation of specimens and concrete damage models, baxsed on the analysis of finite element in linear and nonlinear domains of control and retrofitted specimens, truss models baxsed on strut and tie method baxsed on load pass were presented and applying nonlinear effects to these models were compared with laboratory results and FEA analysis results. The results of strut and tie analysis show that the nonlinear model of strut and tie method has a great potential in predicting the behavior of joints with different details in the joint and in retrofitted specimens as a very powerful tool at the disposal of a design engineer. It can implement seismic design approaches and philosophy baxsed on nonlinear strut and tie methods. Also the results of nonlinear strut and tie method and finite element analysis show that 5% and 10% force such as bond yield and 14% and 40% stiffness of the specimens are compared with the experimental results.