Effects of strain hardening of reinforcement on flexural strength and ductility of reinforced concrete columns

In the evaluation of flexural strength of reinforced concrete (RC) columns, the elastic-perfectly plastic constitutive model is generally used for steel reinforcement, which ignores the strain hardening effect. While some engineers believe that the flexural strength so obtained is on the safe side, others are concerned that underestimation of member strength could lead to inaccurate prediction of overall structural behaviour especially under extreme events. In any case, better understanding of the possible over-strength and its effects on flexural ductility and failure mechanism is necessary. In this paper, the effects of strain hardening of reinforcement on the flexural strength and ductility of reinforced normal- and high-strength concrete columns are studied based on rigorous full-range moment-curvature analysis. The study has identified if and how various parameters affect the strain hardening effect, which include axial load ratio, concrete strength, confining stress, reinforcement ratio and the tensile-strength-to-yield-stress ratio of steel. The effects of strain hardening can be quite significant for RC columns under relatively low axial load and relatively high confining stress. Copyright (C) 2009 John Wiley & Sons, Ltd.