Load Bearing Capacity Of Corroded Reinforced Concrete Beams Under Repeated Loading

Calculation of bearing capacity of corroded members is the key to the durability assessment of reinforced concrete (RC) structures. Concrete structures in practical engineering may be subjected to repeated loads as well as static loads. Load bearing capacity of corroded RC beams under repeated loading was investigated both theoretically and experimentally. A theoretical model was developed based on the relation between hysteresis coefficient of strain in the steel and degradation of bond strength, for the load bearing capacity of corroded RC beams. The model reflects the mechanical characteristics and failure mechanism of the beam under static and repeated loading. The model was developed based on force balance and compatibility of deformation in corroded beams, with consideration given to the influences of such factors as degradation of bond strength, disagreement of the assumption of plane cross-section, strain-hysteresis of reinforcing steel bars, the reduction of steel yield strength and elasticity modulus etc. Formulas were developed for the calculation of midspan deflection and flexural rigidity for corroded beams, with consideration given to the influences of steel corrosion and repeated loading. A total of fifteen test samples, including three non-corroded and twelve corroded RC beams, were experimentally investigated for the comparison with the results from the theoretical model. The effect of steel corrosion on RC beams were evaluated with respect to the deflection, cracking, stiffness, bearing capacity and failure shape under repeated loading. Results or findings from theoretical analysis and the experiments resulted in the following conclusions: (1) It was demonstrated that width and spacing of bending cracking of corroded RC beams increased with steel corrosion level under repeated loading.(2) The flexural rigidity of corroded RC beams under repeated loading rapidly decreased in the cracking stage, with no significant change observed thereafter in the yield stage, when eventually decreased again in the failure stage. The flexural rigidity curve obtained from the tests was similar to that from Neild and Williams.(3) The strains in steel and the surrounding concrete were not found to agree with the plane cross-section assumption. The hysteresis coefficient of strain in the steel increased with the corrosion level, but did not change with loading history.(4) The results from the tests showed that when steel yielded the residual deflection at the midspan of the beams was about 3% of that when the beam finally failed.(5) If no stress peak within the loading history appeared, a limited number of repeated loading had no substantial impact on bearing capacity,and therefore steel corrosion level was the primiary factor which had effect on the load bearing capacity.