混凝土双轴抗压疲劳累积损伤规律试验研究

EXPERIMENTAL STUDY ON THE CUMULATIVE FATIGUE DAMAGE OF PLAIN CONCRETE UNDER BIAXIAL COMPRESSION

本文在对混凝土立方体试件进行定侧压下双轴等幅与变幅抗压疲劳试验的基础上,研究了素混凝土双轴抗压疲劳累积损伤性能。通过对试验结果的分析,证明Miner准则不适于描述疲劳损伤的累积规律;CortenDolan损伤公式可以用于混凝土剩余疲劳寿命的预测。分别选择疲劳最大应变、疲劳残余应变、疲劳变形模量和横向超声波速定义了损伤,得到了不同的损伤累积规律;在综合了纵向变形、模量及横向微裂缝的发展程度的基础上提出了混凝土平均损伤变量,得到了损伤演化方程。本文还应用二级变幅疲劳试验结果修正了常用的损伤等效原理,大大提高了混凝土剩余疲劳寿命预测的精度。本文的研究为混凝土在定侧压下双轴抗压疲劳寿命的预测和损伤评价奠定了基础。

A study on the cumulative fatigue damage of plain concrete under biaxial compression is conducted basing on the experiments of concrete specimens subjected to constant and variable amplitude cyclic loading with constant confined pressure. The present study indicates that the fatigue failure is greatly influenced by the magnitude and sequence of applied variable-amplitude fatigue loading, and Miner's rule is inapplicable to predict the residual fatigue life, especially in ascending order of magnitude; The present research also shows that the exponent d in the Corten-Dolan's formula is a constant relying on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. In addition, the longitudinal maximum strains, residual strains, deformation modulus of concrete and the ultrasonic pulse velocity are used to define the damage, which induces different cumulative fatigue damage laws. An average damage variable is proposed for taking into account all of factors mentioned above, and the cumulative damage law and its evolution are obtained. The equivalent cumulative damage theory is also modified to predict the residual fatigue life of concrete under variable amplitude cyclic loading.