Size Effect on Shear Strength of Reinforced Concrete: Is CSCT or MCFT a Viable Alternative to Energy-Based Design Code?

After sketching the history of the size effect models for the shear strength of reinforced concrete (RC) in design codes, the energy-based size effect law (SEL), recently incorporated into the American Concrete Institute (ACI) design code articles for beam shear and slab punching, is briefly discussed. A general derivation of the SEL based only on the first principles involving energy conservation and dimensional analysis (or laws of similitude) is presented. Attention is then focused on recent articles that present a severe critique of the SEL and various arguments in support of the Muttoni et al.'s critical shear crack theory (CSCT)-an update of the Collins et al.'s modified compression field theory (MCFT)-that some researchers propose to be introduced into the fib Model Code and the Eurocode as an alternative to the SEL. In a point-by-point analysis, it is shown that this critique and these arguments are incorrect and baseless. It is hoped that the present clarification would lead to progress in design codes, enhancing the safety and efficiency of RC structures. (c) 2020 American Society of Civil Engineers.