混凝土直拉、劈拉、弯拉强度关系的试验与仿真研究

Study on the direct tensile,splitting and flexure strengths of concrete

为研究混凝土直拉、劈拉、弯拉强度关系,本文采用静动力试验和数值仿真方法进行对比研究。静力试验中使用液压伺服机完成轴向拉伸、劈裂抗拉和弯曲试验,得到3种抗拉强度关系。试验结果表明直拉强度和劈拉强度相近,低于弯拉强度,符合基于大量试验结果总结的经验关系。数值研究基于混凝土细观颗粒元模型对不同抗拉强度进行仿真,数值结果和试验结果符合良好,并证明受拉断面受力不均匀是弯拉强度高于直拉和劈拉强度的原因。此外,基于该模型进行不同速率的动力加载,得到直拉、劈拉和弯拉强度的率效应——动力增强系数,并和相应的动力试验结果进行了对比。弯拉强度的应变率效应高于直拉和劈拉强度,原因是在动力弯曲试验中动能、摩擦能等其他耗能大幅增加。

Three different methods, i.e. uniaxial tension, splitting and flexure tests, are generally applied for determination of the tensile strengths of concrete. This paper presents experimental and numerical analyses for studying the effects of different methods on static and dynamic tensile strengths. In the static tests, the uniaxial, splitting and flexure strengths are tested using hydraulic-servo machine. The test results conform to the experience relation that the flexure strength is larger than the others. The meso-scale particle element model （PEM） of concrete is used for simulating these three categories of test methods. The numerical results match well with the corresponding experiments and conclude that the different stress states, i.e. uniaxial state for uniaxial tension, muhiaxial state for splitting, and non-uniform state for flexure tests, account for the difference between these strengths. In addition, dynamic increase factors （DIF） determined by different test methods are also analyzed and compared with dynamic test results. The results show the enhancements of strengths are evident but the rate sensitivities determined using different methods vary. The flexure strength of concrete is more significant in the increase of strain rate effect than uniaxial tensile and splitting strengths because of the significant increase of energy consumption, especially the kinetic and frictional components in the dynamic flexure test.