Based on the statistical damage theory,an orthotropic statistical damage constitutive model is pro-posed. In this model, the constitutive behavior of concrete under complex stress state is regarded as the combination of uniaxial tension and uniaxial compression, which are considered as the most fundamental macro failure forms, and the two meso-scale damage modes, rupture and yield are considered. A novel equivalent strain hypothesis is proposed. The equivalent relations between the damage evolution process of complex stress state and uniaxial stress state are established,by introducing the concept of equivalent trans-fer tensile damage strain and the damage influence parameters. Comparison of the prediction results with ex-perimental data shows that it can accurately predict the constitutive behavior in the uniform damage phase for concrete under multiaxial stress states. The damage mechanism is discussed from the view points of the deformation characteristics,strength properties and failure modes.%基于统计损伤理论，本文建立了混凝土三维正交各向异性统计损伤本构模型，用于描述混凝土复杂荷载环境下的力学行为。该模型将单轴拉伸、压缩作为最基本的宏观破坏模式，复杂应力状态下的本构行为理解为2种基本模式的组合形式，考虑断裂、屈服两种细观损伤机制。提出新的“等效应变”假设，通过引入等效传递拉损伤应变和损伤影响参数，建立起复杂应力状态损伤演化过程与单轴损伤演化过程之间的等效关系。通过预测值与试验结果比较，表明该模型能够模拟多轴加载情况下材料均匀损伤阶段本构行为的主要力学特征，从变形特性、强度特征和破坏形式等角度对材料的损伤机制进行探讨。
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