Abstract

A source of confusion in design codes is that multiple equations are often provided for concrete tensile strength, for example one for modulus of rupture and another for direct tension strength. This paper proposes that these differences in tensile strength result from a size effect that is based on the volume of concrete in tension. Volumes larger than about 30 litres (1 ft3) do not show this size effect and crack at the stress recommended by ACI for diagonal web-shear cracking. For smaller volumes the tensile stress at cracking can be up to three or more times larger than this value. When the volume of the specimen is accounted for by the presented empirical size effect equation, the different test methods show consistent results. Using a set of 511 tension tests on plain or reinforced specimens of different types and sizes, the proposed unified tension model is justified. Finally a simple design equation for flexural cracking will be presented.

Biography: Evan C. Bentz, is Professor and Associate Chair (undergrad) of Civil Engineering at the University of Toronto, Canada. He received his BASc from the University of Waterloo, Canada, in 1994 and his PhD from the University of Toronto in 2000. He is a member of ACI Committee 365 service life modelling, and 445, Shear and Torsion. He received the 2007-8 Henry Adams Award, the ACI Chester Paul Seiss Award in 2018 as well as the ACI Design Award twice.