Fracture mechanical prediction of transitional failure and strength of singly-reinforced beams

Experimental observations are compared with approximate nonlinear fracture mechanical predictions of the ultimate capacity of three-point bend, singly-reinforced concrete beams without shear reinforcement. The superposition model is found to provide a better estimate of the shear strength in diagonal tension failure than the size effect model. Moreover, Carpinteri's model based on a transitional brittleness number, a zero crack opening condition (delta = 0) and a fracture toughness accounting for slow crack growth appears to be in good agreement with the observed failure mechanisms and ultimate (and residual) strength in the case of ductile (and brittle) flexural failure, although the test results indicate that a non-zero crack opening condition (delta not equal 0) would improve the prediction, especially for lightly reinforced beams.