Despite the large volume of work reported on the behaviour of reinforced concrete joints, only a few studies have been carried out to investigate the influence of retrofitting joints by FRP composites on the overall behaviour of an RC frame. To study the seismic performance of Moment Resisting RC frames retrofitted at joints by FRP, experimental and numerical investigations are carried out on a scaled-down frame of weak-beam, strong-column type, retrofitted by applying the FRP laminates at the web of the joints. Representing constitutive models are used to introduce the behaviour of concrete, steel and fibre-reinforced polymers in the numerical investigation. Full post-peak behaviour of the joints is captured considering strain softening of concrete. Finite element results show good agreement with the experimental findings. It is found that the maximum load carrying and displacement capacities of the joint after strengthening are increased and that the first steel yielding and development of crack occur at higher loads, further away from the joint, into the beam. The effects of different values of fracture energies on the behaviour of the reinforced concrete joint are also investigated. Nonlinear pushover analyses are also carried out to predict the seismic performance of an eight-storey and two additional low-rise frames retrofitted by steel braces and FRP. It is shown that by using FRP laminates at the web of the joints, the stiffness, the behaviour factor, R, performance level and the lateral load-carrying capacity of the damaged/plain frame are markedly increased.