Continuing the experiments on the double-edge notched pecimens on which the mode Ⅱ fracture toughness KIIc of concrete was measured, a practical testing approach to determine mode Ⅱ fracture energy GIIF is studied using the same geometry.

Based on the complete fracture process in concrete, the crack extension resistance associated with the cohesive force on the fictitious crack is investigated in detail for standard three-point bending notched beams. Five concrete materials are speci

Assuming the weakest link concept. A probalilistic model of fracure in concrete structures has been developed in terms of the critical stress intensity factors. The probabilistic model, wodel, which is expressed in the form of the Weiball distribution, has been compared with arange of experimental results in the literature. The results predicted by the formula are in good agreement with the values reported in the literature for four test secimen geometries-compact tension spectimens, notched three-point bend specinens, wedge splitting spectimens and compact compression specimens. The results presented in the paper have been applied to predict the fracture in large concrete dams and the results compare favourably with observed craking.

The edoubIe-e notched no: ched specimen made of normal s: rengrh tin, crete has been stlbsected to compressive loads, kis shown that a shear crack develops at the notch tip. Visual observation and evaluation of displacement measurements have proven that this specimen allows pure mode I testing, It was possible to determine fracture toughness KIIc, Recommendations for the testing are made.

A simplified method for determining the double-K fracture parameters Kini Ic and Kun Ic for three-point bending tests is proposed. Two empirical formulae are used to describe the crack mouth opening displacement CMOD and the stress intensity factor Kc I caused by the cohesive force σ(x) on the fictitious crack zone for threepoint bending beams. It has been found that the two empirical formulae are accurate for a large practical region of a/D. Experiments carried out by many researchers showed that the new formula of CMOD for three-point bending beams can be directly used to predict the initial crack length for precracked beams, the notch depth and the critical effective crack length, as well as the crack length in the post-critical situation with a satisfactory accuracy. Further verification is demonstrated to determine the double-K parameters Kini Ic and Kun Ic. They are very close to those determined by the method proposed in our previous work. Using the simplified procedure, the experiments can be performed even without a closed-loop testing facility and the calculation can be carried out on a pocket calculator.