The paper gives a detailed description of strengthening of reinforced concrete beams with CERP materials. A review of the building structure, the results of monitoring its technical state and the methods used to strengthen it are included. The strengthened beams are a part of an industrial hall roof support structure. The beams were strengthened with pretensioned carbon fiber strips in flexure and composite fabrics in shear. It was the first implementation in Poland of strengthening an RC structure by pre-stressing with CFRP strips. Nonlinear FEM analysis has been used to evaluation the effectiveness of strengthening method.