Prediction of Reinforcement Tension Produced by Arch Action in RC Beams

In this study, 16 reinforced concrete (RC) simple-span beams were tested statically up to failure to quantitatively investigate the arch action. Variables included four shear-span ratios (2, 2.5, 3, and 4), two longitudinal steel ratios (1 and 2%), and the presence or absence of stirrups. The measured longitudinal reinforcement tensions in the shear span were significantly higher than the calculated values by beam theory. This may be attributed to the reduction of the internal moment arm length by the development of the arch action. The measured steel tension in a shear span was resolved into two components—one for beam action and one for arch action. After reaching the cracking load, the ratio of steel tension from arch action to that from beam action was constant, ranging from 0.2 to 1.2 at the center of the shear span. At ultimate load, over the entire length, the reinforcement force in the beams without web reinforcement and with shear span-to-depth ratio smaller than 3 was almost constant because the beams acted as tied arches. On the basis of the experimental findings, an equation is proposed to predict the internal moment arm length, which then leads to a new method to calculate the steel tension.