An investigation of the minimum web reinforcement requirements for slender and non-slender beams

Abstract

Prescriptive shear requirements from ACI 318 (2019), AASHTO LRFD (2020), and the fib Model Code (2010) stipulate that both slender and non-slender beams must satisfy a minimum web reinforcement requirement. At the very minimum, slender beams require an area of web reinforcement equal to 0.08% of the cross-section placed in the vertical direction, while non-slender beams require up to 0.3% in both the vertical and horizontal directions. This investigation aims to evaluate these minimum web reinforcement requirements in terms of the strength and serviceability behavior of beams based on the results of experimental test data. Databases of shear tests on slender and non-slender beams with web reinforcement is compiled from existing, validated and peer-reviewed datasets. The aim of this study is accomplished through an analysis of these databases. Given the context of this investigation and available data, the results show that a minimum web reinforcement of at least: 0.08% for beams with a f′c 4,000-psi for ACI 318 (2019) is an adequate amount to ensure that the predicted shear strength will be greater than or equal to the experimental shear strength of slender beams, consistent with the recommendations of MacGregor and Hanson (1969) and Roller and Russell (1990); √(f_c^' )⁄f_v for the shear strength of slender beams for AASHTO LRFD (2020) and the fib Model Code (2010), consistent with the results of Shahrooz et al. (2011); 0.12% for the strength of non-slender beams; and 0.25% to restrain cracks widths to less than or equal to 0.016-inches for ACI 318 (2019), AASHTO LRFD (2020), and the fib Model Code (2010) for slender and non-slender beams. Based on these findings, the minimum web reinforcement for strength is consistent with that of the code for slender beams but not deep beams, and the minimum web reinforcement for serviceability is consistent with that of the code for neither slender nor non-slender beams. The prescriptive web reinforcement requirements for slender and non-slender beams do not appear to be derived from the same criteria—at least in the American building and bridge codes. The minimum web reinforcement requirement for slender beams is likely derived based on these members achieving their predicted strength, while the requirement for non-slender beams is likely derived based on these members exhibiting crack widths less than or equal to 0.016-inches while in service