混凝土细观损伤模拟与数值尺寸效应研究

The constitutive law of concrete defines the functional relation between stress and strain and plays a fundamental role in the analysis of structures. However, except for several remarkable progresses, the constitutive modeling and nonlinear analysis of concrete structures still remain quite challenging. In recent 20 years, the rapid developments of damage mechanics, computational solid mechanics and multi-scale theories lead to a paradigm shifting for the constitutive modeling of concrete and lay a solid foundation for the proposed investigation..Based on the systematic experimental observations, the mesoscopic random structure of concrete is investigated and modeled with appropriate numerical descriptions. Then by introducing the newest mesoscopic methods of computational solid mechanics, the stochastic propagation of the mesoscopic crack group could be simulated accurately. To solve the stochastic damage evolution in the macro-scale, the bridging vehicle spanning between the mesoscopic crack propagation and the macroscopic damage evolution is investigated based on classic homogenization theory, while the multi-scale stochastic damage model could be established with the stochastic damage evolutions informed from the meso-scale. Based on the proposed model, the nonlinear behaviors of concrete structures are numerically investigated. In particular, the issues of size effects, which could not be well tackled by the conventional structural simulating methods, are addressed in our research..The proposed research enriches the constitutive theories of solid and offers an alternative way for the analysis and design of concrete structures.

在混凝土细观随机结构实验观测的基础上，深入研究混凝土细观结构的组成特点，建立合理的混凝土细观结构的描述方法；在此基础上，基于固体计算力学最新发展的细观模拟方法，精细模拟混凝土细观裂缝群的产生和发展过程，研究混凝土细观应力随机重分布规律；基于多尺度理论，选取合适的状态变量作为尺度间的桥梁，从细观数值模拟结果出发求解宏观损伤随机演化规律，并与多维连续损伤模型相结合，构成多尺度随机损伤模型的完整体系；采用所建立的多尺度随机损伤模型模拟混凝土结构的全过程非线性行为，有针对性地探索尺寸效应等传统结构非线性分析难以处理的问题，为结构非线性分析与设计提供理论工具与技术支持。

混凝土的细微观结构对材料的宏观损伤演化有着显著的影响，而混凝土材料损伤的产生和发展是结构发生动力灾变的根本原因之一。本项目研究从混凝土的微-纳观结构出发，采用现代试验技术测试了混凝土微-纳观结构的力学性质。基于随机场理论，对混凝土的微-纳观试验数据进行了详细的解构和分析，提取了混凝土细观随机结构的分布和相关特性，进而为基于随机谐和函数方法进行混凝土细观断裂随机场的建模提供了控制参数取值。引入内聚单元方法对混凝土细观断裂随机场进行离散，对混凝土的细观力学行为进行了精细的数值模拟。进而基于多尺度理论，提出了多尺度能量积分，基于混凝土细观数值模拟结果得到宏观损伤演化，研究了宏观损伤演化与单元体几何尺度的依赖性，发展了数值尺寸效应的概念。最后，利用基于细观分析结果得到的多尺度损伤演化规律进行结构的宏观动力灾变模拟。特别研究了苏州中南中心等超高层结构在强震作用下的非线性行为和倒塌全过程。通过本项目研究，混凝土多尺度损伤理论已经基本成型，并且在结构分析和模拟中取得了应用。