According to the Mode Ⅱ fracture test results of concrete of the double-edge notched specimens with four-point shear loading and half symmetrical loading

the relationship of the Mode Ⅱ fracture toughness between two type of concrete specimens was analyzed.Based on the numerical simulation

the stress field near the crack tip was analyzed by use of the finite element method

and the Mode Ⅱfracture toughness of the two types of concrete specimens was calculated with the displacement extrapolation method

and the difference with the experimental results was studied.Because there is the uniform stress in the specimen with half symmetric loading

and the shear stress in the fracture process zone is much larger than the first principal stress during the entire test process

while the phenomenon of opening and torsion of the surface of cracks may appear at the four point shear loading conditions

these factors lead to that the fracture process of the specimen is not always the Mode II fracture of pure shear.