高应力往复荷载下大坝混凝土动态轴拉力学特性及损伤机理

The dynamic characteristic of dam concrete is the weak link for the seismic evaluation of the hydropower project construction. Under the earthquake, the tensile behavior of dam concrete is the research focus during the dynamic characteristic, and the uniaxial tensile test is the direct method to determine the dynamic tensile behavior of dam concrete. In the project, the dynamic uniaxial tensile experimental techniques on the large size specimens (300 mm diameter and 600 mm height) of the dam concrete will be studied, and the measuring method for the dynamic uniaxial tensile characteristic of dam concrete under high stress repeated loads will be obtained. Considering the four factors of the maximum stress level, stress amplitude, loading rate and initial loads, the experimental work on the dynamic uniaxial behavior of dam concrete will be carried out, and the evolution laws for the dynamic mechanical characteristics of dam concrete will be investigated. Based on the analysis of the experimental data and considering the "rate effect" and "repeated effect", the predicted model for dynamic uniaxial damage will be established and verified. The damage mechanisms for dam concrete under dynamic uniaxial tensile loading will be presented. Finally, based on the predicted model for dynamic damage, the predicted model for the ultimate tensile strain of dam concrete under high stress repeated loading will be established. The research in this project has great theoretical significance and application value to the seismic safety evaluation of dam structures.

大坝混凝土动态抗力是目前水利水电工程建设抗震安全性正确评价的薄弱环节。在地震作用下，大坝混凝土动态力学特性研究的重点是其抗拉特性，而轴向拉伸试验是确定其抗拉力学特性最直接的方法。本项目拟通过对大试件(直径300mm，高度600mm)大坝混凝土动态轴拉试验技术进行研究，得到高应力往复荷载下大坝混凝土动态轴拉力学特性的测定方法。然后考虑最大应力水平、应力幅值、加载速率及初始荷载四个影响因素，进行高应力往复荷载下大坝混凝土动态轴拉试验研究，探寻各种荷载工况下大坝混凝土轴拉力学特性的演化规律。分析提炼所获试验数据，考虑“率效应”及“往复效应”，构建并验证高应力往复荷载下大坝混凝土轴拉损伤预测模型，探寻与区分高应力往复荷载下大坝混凝土动态轴拉损伤机理。最后，在损伤模型基础上构建并验证高应力轴拉往复荷载下大坝混凝土动态极限拉应变的预测模型。本项目研究对大坝抗震安全性评价具有重要理论意义和实用价值。

大坝混凝土结构在地震荷载作用下的失效，通常体现为混凝土结构的严重开裂扩展。地震荷载通常表现为不同振幅、不同速率的周期振动，混凝土材料发生失效时，应力水平通常较高。因此，对大坝混凝土高应力水平下轴拉疲劳特性的研究尤为重要。本项目围绕大坝混凝土结构在地震荷载作用下开裂扩展破坏这一工程问题，针对大坝混凝土开展了不同应力水平、不同加载频率和不同加载次序的高应力循环轴拉试验。结果表明，加载应力水平一定时，频率越大，循环破坏次数也越大；循环破坏次数随加载应力水平的增大而减小，随加载频率的增大而增大。弹性模量、残余应变、最大应变的演化表现为S形三阶段规律。循环次数与平均耗散能呈幂函数关系。低-高加载次序混凝土累积循环破坏次数比M＞1，相反，M＜1。基于连续损伤力学理论提出改进的混凝土损伤演化模型，利用损伤模型实现了对变幅循环轴拉荷载下混凝土的剩余破坏次数的预测。本项目研究对大坝抗震安全性评价具有重要理论意义和使用价值。