Effect of uniform load on the shear strength of slender beams without shear reinforcement

Previous studies have shown that a uniform distribution of load may increase the shear strength of a slender member by as much as 40 percent (Leonhardt and Walther 1964). The increase of shear strength is potentially due to clamping stresses induced from the uniform load, although a mathematical equation to quantify the effect of clamping stress in slender uniformly loaded members has yet to be derived (Acevedo et al. 2009). Only a small percentage of all shear tests on slender specimens without shear reinforcement were completed with uniform load. Additionally, the majority of uniform load data consists of specimens with small specimen depths (d) and large longitudinal reinforcement ratios (ρ). Six shear tests on specimens without shear reinforcement were completed at the University of Texas at Austin. Three of the six specimens were subjected to concentrated load, and the remaining three companion specimens were loaded uniformly. These specimens are among the deepest slender members without shear reinforcement that have ever been tested under a uniform load distribution. Importantly, the ratio of maximum shear to maximum moment was maintained between concentrated and uniform load tests which ensures directly comparable tests results. The experimental results were shown to be influenced by load distribution. Uniformly loaded specimens had an average increase in first diagonal cracking shear capacity of 17 percent with a range of increase between 10 and 23 percent when compared with specimens subjected to concentrated loads.