Effect of relative stiffness on moment redistribution in reinforced high-strength concrete beams

Abstract

Moment redistribution in continuous concrete beams is primarily a structural aspect of behaviour, since it is a consequence of structural redundancy. However, the current design codes do not take this structural characteristic into consideration and therefore may not be reasonable when predicting the permissible moment redistribution. In this paper, moment redistribution in reinforced high-strength concrete (HSC) beams is analysed, focusing on the effect of relative stiffness represented by the structure-related parameter ρs2/ρs1 (where ρs1 and ρs2 are the tensile steel ratios over positive and negative moment regions, respectively). A numerical evaluation was conducted on two-span continuous beams made of HSC having a cylinder compressive strength of 90 MPa. A wide range of ρs2/ρs1 was produced by varying either ρs1 or ρs2 from 0·81% to 6·06%. The results show that the ρs2/ρs1 ratio is a critical parameter influencing the global moment redistribution behaviour. Modifications to the Canadian Standards Association and American Concrete Institute equations are proposed for calculating the moment redistribution at the ultimate state. By introducing the parameter ρs2/ρs1, the proposed modified equations are shown to have an excellent fit to the actual redistribution values.