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-or<br />high-strength concrete have been evaluated using a newly developed analytical method that takes into<br />account the stress-path dependence of the constitutive properties of the materials. From the moment-curvature<br />curves and the strain distribution results obtained, the post-peak behavior and flexural ductility<br />of doubly reinforced normal- and high-strength concrete beam sections are studied. It is found that the<br />major factors affecting the flexural ductility of reinforced concrete beam sections are the tension steel<br />ratio, compression steel ratio and concrete grade. Generally, the flexural ductility decreases as the amount<br />of tension reinforcement increases, but increases as the amount of compression reinforcement increases.<br />However, the effect of the concrete grade on flexural ductility is fairly complicated, as will be explained<br />in the paper. Quantitative analysis of such effects has been carried out and a formula for direct evaluation<br />of the flexural ductility of doubly reinforced concrete sections developed. The formula should be useful<br />for the ductility design of doubly reinforced normal- and high-strength concrete beams.