真三轴应力下塑性混凝土性能及破坏准则

Performance and failure criteria for plastic concrete under true tri-axial compressive stress

基于5组配合比共45组塑性混凝土立方体试件的真三轴试验，研究了塑性混凝土的力学变形性能和破坏准则。结果表明，塑性混凝土第一主应力一应变关系曲线可分初始反弯段、直线段、曲线段和直线平台段，其中初始段有明显的弹性特征，直线段之后塑性变形较大。当第二、第三主应力较小时，真三轴应力下塑性混凝土试件破坏形态与单轴受压相似，当第二、第三主应力较大时，试件破坏呈现八字形斜裂缝。第一主应力随第二、第三主应力的增加而增大，且对第三主应力的变化较为敏感；对于同组配合比的塑性混凝土，固定第二主应力、变化第三主应力时的黏聚力和内摩擦角与第二和第三主应力同时成比例增加时的黏聚力和内摩擦角相比，分别是2倍和0．5倍左右；塑性混凝土三轴抗压强度是单轴抗压强度的3—5倍。在此基础上，运用强度理论分析了本文及文献的试验数据，建立了真三轴应力下塑性混凝土的二参数、三参数和四参数破坏准则，并与普通混凝土进行了比较。

Based on the tests for 45 groups of plastic concrete specimens with five mix proportions under tri-axial compressive stress, the characteristics of the plastic concrete under true tri-axial test were ana- lyzed. The results indicate that the first principal stress-strain curves of plastic concrete can be broadly di- vided into four sections including the initial contra flexural section, straight line section, curve section and straight-line platform section respectively, in which the initial segment appears significantly elastic character- istic and the last segment after the straight line section reflects severely plastic property. Specimen failure pattern is similar to axial compression failure pattern when the second and third principal stress are smaller and is shown as the diagonal cracks when they are larger. The first principal stress increases with the in- creasing of third principal stress or the second principal stress; the changing of the third principal stress has the influence on the first principal stress obviously. Cohesion and angle of internal friction at the condi- tion that third principal stress increases when the second principal stress is fixed are respectively about 2 and 0.5 times of those when the second principal stress and the third principal stress both increase at fixed ratio. Tri-axial compressive strength is 3-5 times of the axial compressive strength for plastic concrete. Based on the analysis of test datum in this paper and from the related literatures by using the relat- ed strength theories, the formulae with two parameters, three parameters and four parameters are put for- ward respectively to express the failure criterion of plastic concrete under true tri-axial compression, and the comparison with ordinary concrete is also conducted.