Shear characteristics of high-strength concrete deep beams without shear reinforcements

Based on the strength at the first diagonal crack of normal-strength concrete and normal beams without the consideration of size effects, the ACI code specifies the shear strength of deep beams. It is necessary to evaluate whether the ACI equation for deep beams is applicable to high-strength concrete deep beams with reinforcement ratio less than 1% and to consider size effects. Twenty-one beam specimens were tested to investigate their shear characteristics with the variables of concrete strength, shear span/depth ratio, and overall depth. The decrease in shear span/depth ratio and the increase in overall depth under the same shear span/depth ratio led to more brittle failure, with wide diagonal cracks and high energy release rate related to size effects. The high-strength concrete deep beams exhibited more remarkable size effects with regard to brittle behavior. It was also shown that the ACI code gives similar safety factors on the shear strength at the first diagonal crack of high-strength concrete deep beams, but do not specify a high enough safety factor on their ultimate strength due to the size effects.