Post-peak behavior and flexural ductility of doubly reinforced normal- and high-strength concrete beams

The complete moment-curvature curves of doubly reinforced concrete beams made of normal-orhigh-strength concrete have been evaluated using a newly developed analytical method that takes intoaccount the stress-path dependence of the constitutive properties of the materials. From the moment-curvaturecurves and the strain distribution results obtained, the post-peak behavior and flexural ductilityof doubly reinforced normal- and high-strength concrete beam sections are studied. It is found that themajor factors affecting the flexural ductility of reinforced concrete beam sections are the tension steelratio, compression steel ratio and concrete grade. Generally, the flexural ductility decreases as the amountof tension reinforcement increases, but increases as the amount of compression reinforcement increases.However, the effect of the concrete grade on flexural ductility is fairly complicated, as will be explainedin the paper. Quantitative analysis of such effects has been carried out and a formula for direct evaluationof the flexural ductility of doubly reinforced concrete sections developed. The formula should be usefulfor the ductility design of doubly reinforced normal- and high-strength concrete beams.