复杂加载路径下大坝混凝土动态轴拉统一损伤本构关系研究

The dynamic characteristic of dam concrete is a weak link for the seismic safety evaluation of the hydropower constructions. 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. How to use the reasonable damage variable and consequently uncover the nonlinearity of dam concrete is the key and urgent issue in the research of dynamic safety of concrete dam. In this project, based on the investigation on the last National Science Foundation of China majored by the applicant, the direct tensile test method on concrete is improved. The direct tensile tests on dam concrete will be carried out under complex loading paths based on the improved method and the tensile behaviors will be analyzed. Combined the macro-meso damage mechanics theory, the damage evolution model based on reduction of unloading elastic modulus of dam concrete will be established. Finally, the yield criterion will be determined based on the plastic theory and a unified time-dependent constitutive model of dam concrete will be established considering the transient strain path. This research provides a theoretical and scientific basis for revealing the anti-earthquake design and safety evaluation of dam concrete structures.

大坝混凝土动态抗力特性是目前水利水电工程建设抗震安全性评价的薄弱环节。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抗拉力学特性最直接的方法。如何确定合理的损伤变量，进而建立合适的混凝土损伤本构模型，揭示大坝混凝土非线性损伤机理，是大坝抗动力安全性评价需要解决的关键基础问题。在申请人所主持的国家自然科学基金青年项目基础上，本项目拟通过改进混凝土轴拉测试方法进而开展复杂加载路径下大坝混凝土动态轴拉试验，分析不同加载路径下大坝混凝土轴拉力学特性变化规律；结合宏细观损伤理论建立基于卸载弹模衰减准则的混凝土损伤演化模型；利用塑性理论构建屈服准则函数，结合试验数据构建考虑瞬时应变路径影响的大坝混凝土统一率型弹塑性损伤本构模型。研究成果为揭示地震作用下大坝结构非线性损伤机理和破坏倒塌机制，以及大坝结构抗震设计及安全性评价提供理论基础和科学依据。

大坝混凝土结构在持续循环荷载作用下会产生非线性损伤累积，准确预测循环荷载作用下混凝土结构的力学性能和损伤破坏过程，对评估大坝混凝土结构的运行安全性具有重要的工程意义。本研究针对大坝混凝土开展了复杂加载路径下的循环轴拉试验，系统探究了混凝土在循环荷载作用下的轴拉力学性能。通过自行设计的可自由转动球铰传力装置和端部粘贴式的试件连接方式实现了以应变控制的混凝土包含峰后段循环轴拉试验，揭示了混凝土的非线性性质和损伤演化机理，确定了同时反映弹模衰减和塑性应变累积的损伤参数，构建了循环轴拉荷载作用下混凝土应力-应变关系模型和非线性损伤演化模型。除此以外，为实现加卸载本构模型，对RDDP有限元程序中的等效节点荷载矩阵模块和材料非线性模块进行进一步完善，实现了混凝土连续卸载、再加载应力-应变曲线的数值仿真。有限元数值仿真应力-应变曲线与理论模型计算结果以及试验结果基本一致，验证了提出的应力-应变关系模型有效性。