Evaluation of Minimum Web Reinforcement Requirements for Slender and Non-Slender Beams

Prescriptive shear requirements in the U.S. from the American Concrete Institute (ACI) 318 (2019), the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) Bridge Design Specifications (2020), and the fédération international du béton Model Code (fib MC) (2010) include a minimum web reinforcement requirement. In general, slender beams require a minimum area of web reinforcement equal to 0.08% of the cross-section, while non-slender beams require up to 0.30%, or roughly three times more than the slender beam requirement. This investigation aims to evaluate the discrepancy between these requirements in relation to the strength and serviceability behavior of experimental test data. This is carried out through an analysis of existing and peer-reviewed databases. The results show that the minimum web reinforcement needed to ensure shear strength is consistent with code requirements for slender beams, but not non-slender beams. The minimum web reinforcement needed to restrain crack widths is consistent with code requirements for non-slender beams, but not slender beams. Thus, the prescriptive web reinforcement requirements for slender and non-slender beams do not appear to be derived from the same criteria. The requirement for slender beams is derived based on these members achieving their predicted strength, while the requirement for non-slender beams is derived based on the width of in-service cracks.