Influence of using moment redistribution and high-strength steels on crack width and deformations

The linear analysis with limited moment redistribution is useful to reduce the maximum negative moments at support sections, bringing this way several advantages to design and execution of reinforced concrete beams and slabs. The maximum moment redistribution is not related only with the plastic rotation capacity of the critical sections, but also with the requirements at the Serviceability Limit States. The main structural concrete codes condition the maximum moment redistribution to the ductility of the sections and to the ductility of the steels used. The goal of this study is to analyze how the limitation of crack width under service conditions affects the maximum moment redistribution used in the analysis to the Ultimate Limit States. On the other hand, with the increasing use of high-strength steels, it is important to assess how this type of steels can limit the moment redistribution and how they influence the crack width. It was found that the maximum moment redistribution is significantly conditioned by the limitation of the maximum crack width and by the q SLS /q ULS ratio, which is the ratio between the load corresponding to the service conditions (q ELS ) and the load used on the verifications of the Ultimate Limit States (q ELU ). In certain situations, the maximum moment redistribution possible was lower than the values recommended by main codes, Eurocode 2 and fib Model Code. To exploit the full capacity of high strength steels, the moment redistribution must be very limited and applied only on structures located in less aggressive environments. To understand all effects of the moment redistribution, a non-linear analysis was also performed to analyze the real evolution of the moment distribution along the beam axis for different load levels. Based on the study performed, it is proposed an empirical equation to predict the maximum moment redistribution allowed, considering all key parameters.