Failure mechanism of corroded RC beams strengthened at shear and bending positions

•A calculation method of the capacity for corroded strengthening beams is proposed;•Corrosion has a small influence on the early stiffness of corroded beams;•The bottom steel plate strengthening improves the early stiffness of corroded beams;•Combined strengthening methods can efficiently exploit the material properties; and.•Combined strengthening beams are vulnerable to the failure of supports. This study proposes a calculation method of the ultimate load-bearing capacity for corroded RC beams strengthened with different methods. Eight experimental beams subjected to electrochemical corrosion are designed and divided into two groups to verify the presented calculation method and investigate the mechanical properties of the strengthened beams. In the first group, U-shape plates with bar are enhanced at the shear zone to improve the shear capacity and prevent shear failures (i.e., A-type beams without the bottom steel plate). In the second group, to improve the shear and bending capacity, a steel plate is strengthened at the bottom of the beam, simultaneously, the U-shape plates with bar are enhanced at the shear zone (i.e., B-type beams with the bottom steel plate). Based on the calculated and experimental results, the mechanical properties, failure modes, and ultimate load-bearing capacity are investigated for corroded RC beams strengthened with different methods. A parametric study is then conducted by considering various strengthening methods and corrosion rates. The results show that: (a) the corrosion reduces the mechanical properties of reinforcements, weakens the adhesion property between reinforcements and the concrete, and speeds up the crack development and the failure of beams, but it has a small influence on early stiffness/deformations of RC beams; (b) the local corrosion damage of the reinforcement cross-section has a vital influence on deformations, ultimate load-bearing capacity, and failure modes of corroded beams; (c) the bottom steel plate strengthening can effectively improve the early stiffness of corroded beams; (d) the combined strengthening of the bottom steel plate and U-shape plates can favorably improve the ultimate load-bearing capacity and ductility of corroded beams, suppress the crack development, and make full use of the compression performance of the concrete and the tensile property of the reinforcements; (e) corroded beams with the shear and bending strengthening are vulnerable to the failure of bearings.