An Experimental Study on the Fracture of Concrete in Flexure

At the first step, the stress-strain relation of concrete in direct tension and in flexural tension were examined. The strain at the beginning of fracture in the former was about 10.6 to 12.2×(10)^<-5> and that in the latter was about 18.2 to 21.5×(10)^<-5>. These results show that the fracture of concrete beam does not start even if the extreme tensile fiber strain represents the strain at which the fracture in direct tension starts. It is assumed that the resistance of concrete beam to external force does not decrease since tensile stresses in inner fibers increase when the extreme fiber fails. Experimental results which prove this hypothesis are presented. The notable change of stress distribution occurred when the extreme tensile fiber strain of concrete beam was over the strain at which the fracture of concrete in direct tension began, but the neutral axis did not move at this time. The rise of the neutral axis began when the extreme tensile fiber strain came to about 18.2 to 21.5×(10)^<-5>, i.e. the strain at the beginning of fracture of concrete beam.