The fiber-reinforced polymers (FRP) were used over the past years to strength the reinforced concrete (RC) beams and slabs by attaching it to their tension face. Despite considerable research over the last decade, reliable model to simulate the performance of strengthened beams still need more research. In this paper, a nonlinear numerical analysis code based on the rigid body spring model (RBSM) was extended to simulate the behavior of (RC) beams strengthened with externally bonded (FRP). The code supports the nonlinear constitutive laws for the different materials and nonlinear bond stress-slip relationships for steel - concrete and FRP-concrete interfaces. Previous experimental programs were used to validate the the model and confirm its ability to simulate the experimental observations. In all cases, very good agreement between the analytical and the experimental observations is obtained in terms of deflections, strains, internal forces, and failure mode, showing the capabilities of the model to evaluate the efficiency of proposed strengthening solutions.