Required plastic rotation of RC beams

Abstract

Linear analysis with moment redistribution has been allowed under codes of concrete structures for a long time. There is, however, still a certain lack of consensus regarding the value of the redistribution coefficients. The calculation of those coefficients ignores the influence of some factors in moment redistribution, and this may lead to designs that exceed the bounds of safety, or, under other circumstances, may result in very conservative designs. This study sets out to analyse the influence of those factors (structure type, load type, concrete strength and beam slenderness) on the value of the redistribution coefficient. The relationship between ä and x/d is determined from the plastic rotation capacity of the critical sections and from the plastic rotation required to obtain a given distribution of moments. The study carried out on the required plastic rotation led to the determination of new relationships between ä and x/d. The proposed equations were compared with MC90 and EC2 equations, and it was concluded that the codes allow larger moment redistribution than was found in this study, especially for the cases in which x/d takes larger values.