ARCH ACTION IN REINFORCED CONCRETE BEAMS--A RATIONAL PREDICTION OF SHEAR STRENGTH

A rational expression, developed to predict the shear strength of reinforced concrete beams, is derived from the relationship between shear and the rate of change of bending moment along a beam coupled with experimental findings for the arch action. Eight reinforced concrete simple span beams without web reinforcement were tested statically up to failure to investigate quantitatively the arch action. Variables included four shear span-to-depth ratios (2, 2.5, 3, and 4) and two longitudinal steel ratios (1% and 2%). On the basis of the experimental findings, an equation is proposed to predict the internal moment arm length, which then leads to a shear strength equation that combines beam action and arch action. The proposed ultimate shear strength equation, arising from analytical premises and then calibrated with experimental data, is a similar form to the American Concrete Institute (ACI) 318 equation derived mainly from an empirical approach. The proposed ultimate shear strength equation applied to existing test data and the results were compared with those predicted by the ACI 318 equation and the Zsutty's equation.