Discussion on “Explicitly quantifying the effect of bond stress on the failure of reinforced concrete membranes” by Fei Geng, Chao Xu, and Zengping Wen [structural concrete, 2023, DOI: 10.1002/suco.202200561]

Abstract

The authors of this paper address the relevant topic of the effect of bonds on the behavior of reinforced concrete elements under in-plane loading, focusing on the compressive stresses in the concrete. They claim that in previous models, “the contribution of bond stress to the compression in the cracked concrete struts was usually neglected” and present a model according to which “for pure shear, the contribution of bond stress to the compressive stress in the concrete is at least two times of the average (apparent) compression.” They further argue that these increased compressive stresses explain the compression softening effect of concrete, rather than the common understanding of a reduced compressive strength due to imposed transverse strains. However, the entire paper, and thus all its conclusions, are built on the ill-founded assumption that bond increases the concrete compressive stresses, while in reality, the concrete compressive stresses are reduced by the bond between the cracks. In addition, the authors' model—apart from being limited to specific situations as it requires coupling of the diagonal compressive struts to the intersections of longitudinal and transverse reinforcement—is based on several other mechanically unsound assumptions. The most severe issues will be clarified in the following discussion.