Minimum flexural ductility design of high-strength concrete beams

Abstract

In the flexural design of reinforced concrete beams, apart from the provision of adequate strength, it is also necessary to provide a certain minimum level of ductility. Traditionally, this has been done by limiting the tension steel ratio or the neutral axis depth to no more than certain fixed maximum values. However, this would result in a variable level of curvature ductility depending on the concrete grade and the steel yield strength. Of greater concern is that this would lead to a lower level of curvature ductility than has been provided in the past to beams made of conventional materials when high-strength concrete and/or high-strength steel are used. It is proposed herein that instead of limiting the tension steel ratio and the neutral axis depth, it is better to set a fixed minimum to the curvature ductility factor. The maximum values of tension steel ratio and neutral axis depth corresponding to the proposed minimum curvature ductility factor for various concrete grades and steel yield strengths have been evaluated. Based on these maximum values, simplified guidelines for providing minimum flexural ductility have been developed.