Study on initial cracking criterion for I-II mixed mode crack and influence of crack-depth ratio in concrete by using four-point shearing beams

An experimental study on initial cracking criterion has been carried out by using four-point shearing beams with three different crack-depth ratios.The maximum loads,the initial loads and crack initiation angles were measured in the experiment.Based on the initial loads measured in the test,the corresponding KⅠ and KⅡ can be calculated using finite element method.Besides,a more rational load distribution under four-point shearing condition was obtained.Finally,a crack initial cracking criterion for I-II mixed mode crack was proposed,which is different from the cracking criterion by using maximum loads,and its crack-depth ratio effect,crack-depth ratio effect on the crack initiation angles,KⅠ /KⅡ were also discussed.The result shows that when crack-depth ratio in the range from 0.3 to 0.4,it has important effect on crack initial cracking criterion for I-II mixed mode crack,while the crack-depth ratio in the range from 0.4 to 0.5,it has little impact.The test results also show that the crack initiation angles increase with the increase of crack-depth ratio.While for KⅠ/KⅡ,it decreases along with the increase of the crack-depth ratio.