Effect of under-reinforcement on the flexural strength of corroded beams

Reinforced concrete beams are normally designed as under-reinforced to provide ductile behaviour i.e. the tensile moment of resistance, M-t(0) is less than the moment of resistance of the compressive zone, M-c . The degree of under-reinforcement (M-t(0)/M-c ratio) can depend upon the preferences of the designer in complying with design and construction constraints, codes and availability of steel reinforcement diameters and length. M-t(0)/M-c is further influenced during service life by corrosion which decreases M-t(0). The paper investigates the influence of M-t(0)/M-c on the residual flexural strength of corroded beams and determines detailing parameters (e.g. size and percentage of steel reinforcement, cover) on M-t(0)/M-c . Corroded reinforced concrete beams (100 mm x 150 mm deep) with varying M-t(0)/M-c ratios were tested in flexure. The results of the investigation were combined with the results of similar work by other researchers and show that beams with lower M-t(0)/M-c ratios suffer lower flexural strength loss when subjected to tensile reinforcement corrosion. Cover to the main steel does not directly influence M-t(0)/M-c and, thus, the residual flexural strength of corroded beams is not normally affected by increased cover. A simplified expression for estimating the residual strength of corroded beams is also given.