Elaboração de Ábacos para Dimensionamento de Pilares com Concretos Classes C40 a C90 Solicitados a Flexão Composta Reta Conforme ABNT NBR 6118:2023

Abstract

In this work, the interaction diagrams of axial load and bending moments were developed for the design of high-strength rectangular elements, in compliance with the code of NBR 6118 (ABNT, 2023). Some changes begin with concrete of class C45, while others only apply to C55. The norm update introduced several differentiations for the ultimate limit state (ULS) of high-strength concretes, due to their brittle behavior. Therefore, to carry out proper designs for these structures, ensuring their safety, it is necessary to develop abaci that conform to the normative changes. For the development, normative standards were adopted, describing equations and parameters such as strain domains and the reduction of concrete stress and ultimate strain. Considering these differences, the approximation of the concrete stress-strain curve was adopted for a rectangular diagram with the parameter λ, thus achieving the equilibrium of the cross-section for the calculation of the resistant forces NR and MR. To generate the abaci, all parameters of the used formulations had to be transformed into dimensionless quantities so that the plotted values would be valid for any rectangular sections following the parameters described in the abaci. In conclusion, it can be inferred that due to the reductions, which increase with the increase in the concrete strength class, the use of very high-strength concretes does not bring significant benefits. This is because the increase in strength does not generate a proportional increase in the resistant forces NR and MR.