Evaluation of shear design criteria of beams according to NBR6118 applying the modified compression field theory

Abstract

It is known that design deficiencies in shear design are more dangerous than bending, as shear failures can occur in a fragile way and without possibility of redistributing internal forces. Unlike bending design, designing for shear loads by different standards can generate significantly different results for the same element, as long as design models have been under discussion for many years. This paper analyses the evaluation of the behavior of the combined bending and shear loads in reinforced concrete beams for different pairs of these forces. For this purpose, the verification presented in ABNT NBR 6118 was used and compared to a more improved theory currently used, the Modified Compression Field Theory - MCFT. This theory is able to predict the relationships of specific loads and strains, as well as the shear strength of sections with great precision, being parameterized by several tested elements. As the use of this theory is not practical for manual calculations, the Response-2000 software, developed at the University of Toronto by Evan C. Bentz, was used. The program allows the analysis of beams and columns subject to moments, shear forces and axial loads, for any type of geometry, material properties and reinforcement arrangement, resulting in accurate responses of the behavior of the sections using MCFT as a basis.