冻融劣化混凝土压剪作用下力学特性及破坏准则

为研究冻融劣化混凝土动静态抗剪性能，进行了不同冻融循环次数(0，10，25，35和50次)后混凝土在不同法向应力(0，3，6，9和12 MPa)下的压剪强度试验，混凝土强度等级为C30。研究分析了冻融循环次数和法向应力对混凝土剪切强度、峰值应变和黏聚力与摩擦系数的影响。分析结果表明:①随着冻融循环次数的增加，混凝土在相同法向应力状态下的剪切强度均逐渐降低，而且法向应力越大，剪切强度随冻融循环次数的增加而降低的程度越小；当冻融循环次数相同且法向应力不大于单轴抗压强度50%时，剪切强度随法向应力的增大而增大，且冻融劣化程度会影响该增幅效果；②在法向应力相同时，剪切峰值变形随冻融循环次数的增加呈线性增长趋势，对某一冻融循环次数，法向应力的存在增大了混凝土的剪切峰值变形；③摩擦系数和黏聚力都随冻融劣化程度的加深而降低，黏聚力大幅度降低是由于冻融劣化作用起主导作用所致。基于上述试验分析和八面体应力空间二次抛物线形式的压剪破坏准则，构建了平面应力状态下考虑冻融循环次数的混凝土压剪破坏准则。

Mechanical properties and failure criterion of freeze-thaw deteriorated concrete under compressive-shear stress

In order to study the dynamic and static shear properties of the freeze-thaw deteriorated concrete, the compressive-shear strength tests on concrete are carried out under different normal stresses (0, 3, 6, 9 and 12 MPa) after different freeze-thaw cycles (0, 10, 25, 35 and 50 times), and the concrete strength grade is C30. The impacts of the freeze-thaw cycles and normal stress on the shear strength, peak strain, cohesion and friction coefficients of concrete are studied. The analysis results show that:① With the increase of the freeze-thaw cycles, the shear strength of concrete decreases gradually under the same normal stress status. The greater the normal stress is, the smaller the shear strength of concrete decrease degree with the increase of the freeze-thaw cycles. When the number of the freeze-thaw cycles is the same and the normal stress is less than 50%of the uniaxial compressive strength, the shear strength increases with the increase of the normal stress, and the deterioration of freezing and thawing will affect the results of this increase. ② When the normal stress is the same, the shear peak deformation increases linearly with the increase of the freeze-thaw cycles. For a certain freeze-thaw cycle, the existence of the normal stress increases the shear peak deformation of concrete. ③ The coefficients of friction and cohesion decrease with the deepening of the deterioration degree of freeze-thaw, and the significant decrease of cohesion is due to the dominant role of freezing and thawing deterioration. ④ On the basis of the above experimental analysis and the compression-shear failure criterion of octahedron stress space in the form of quadratic parabola, a compression-shear failure criterion of concrete considering the number of freeze-thaw cycles in plane stress state is established.