| Moment redistribution provides an attractive alternative to the non-linear methods of analysis. CSA A23.3-94 provisions for moment redistribution neglect the effects of important parameters and can be conservative. Significant differences exist among design standards on the provisions for moment redistribution. The lack of consensus suggests that as a profession we do not fully understand the problem. This work attempts to establish appropriate limits on allowable moment redistribution in reinforced concrete structures.; An analytical model is developed for computing beta, the permissible percentage reduction in moment at a section due to moment redistribution. Important parameters affecting beta are identified and incorporated in the model. The model is validated against experimental results and shows good agreement. Comparison between CSA A23.3-94 and the model limits shows that the code is conservative. The maximum code limit for beta is 20%. For the ultimate limit-state, with favourable combination of parameters, the model would allow beta in excess of 50%. The serviceability limit state, however, can restrict beta to 21% to 34%.; The code considers beta as a function of c/d, the ratio of the depth of neutral axis to the effective depth of beam cross-section, only. For 20% moment redistribution, the standard allowable c/d is only 0.2. By comparison, the model allowable c/d for 20% moment redistribution is at least 0.38 and can be as high as 0.6.; A parametric study shows that the beta depends upon various parameters, in addition to c/d. It is thus inappropriate to express beta as a function of c/d alone.; A set of empirical equations for beta is developed to provide an alternative to the code equation. The equations consider the explicit effects of o, the mechanical reinforcement ratio, and L/d, the span to depth ratio, on beta, with implicit effects from other parameters.; Design moment coefficients for continuous reinforced concrete beams are developed. Use of these coefficients vs. code coefficients can provide savings in the amount of flexural reinforcement. It is demonstrated that considering moment redistribution can eliminate the need for pattern live-load analysis, in the design of continuous reinforced concrete beams with c/d less than 0.4. |
