中文摘要：

在混凝土微平面本构模型M2的基础上，将微平面上的应力分解为体、偏、剪三个分量，与原有模型定义的微平面各分量应力一应变关系不同，通过分析各个分量的物理意义，定义了相应的应力一应变关系函数，即理想弹塑性函数。引入了破断应变的概念，当微平面应变达到破断应变后应力减为零。在此基础上，提出了钢钎维微平面模型，使得模型可以考虑钢纤维对混凝土的加强作用，并对已有单轴压缩和单轴拉伸试验数据进行拟合，结果表明，微平面本构模型能够较好模拟混凝土应力软化段，初步验证了本文所建议模型的合理性和正确性。

英文摘要：

A dynamic elastic-plastic microplane constitutive model for concrete based on M2 is presented in this paper. The state of each microplane is characterized by normal deviatoric, volumetric strains and shear strain. The strain-stress relations for deviatoric and shear component are described as elastic-plastic model which is different from original model. The corresponding strain-stress relations function is defined by analyzing the physical meaning of each component, namely ideal elastic-plastic function. A new concept, failure strain, is introduced, in such case if strain component on microplane exceeds failure strain, the stress will be zero. In order to take account of the reinforced effect of steel fiber on concrete, the microplane model for steel fiber reinforced concrete is suggested based on the improved microplane model proposed in this paper. Finally two calculation examples, under uni-axial conpression and under uni-axial tension, have been adopted to verify the rationality and correctness of the model. The results show that the model proposed in this paper can properly simulate the stress softening of concrete.