载荷与环境作用下氯离子侵蚀与混凝土开裂过程耦合分析方法及应用

Chloride-induced corrosion of steel reinforcement has been identified as one of the main causes of deterioration of concrete structures. The present mainstream of studies on concrete durability is an interdisciplinary research by combining the advances on materials science, structural science and mechanics. A comprehensive model is proposed to take damage prognosis on concrete structures and to analyze its sustainability under loadings and environmental effects. Further studies will be tackled to explore the temperature, dry-wet circulation, surface chlorine ion concentration and the geometric shape of cracks in the influence mechanism of the chloride ion erosion process. The evolution of non-uniform damages in concrete also will be revealed. .With the concrete reinforcement corrosion model, the discrete element method (DEM) and extended finite element method (XFEM) will be used to study the mechanisms of cracks initiation, expansion and stability, and their perturbations caused by the random distribution of coarse aggregates and coherence interface layers in concrete. Combined with the accelerated destruction test of concrete structures under loadings and chloride penetration, the spatial distribution model of cracks and their evolutions within concrete should be established. The model of concrete apparent diffusion coefficient containing the effects of cracks propagation process should be constructed via experimental observations and theoretical derivation, and the nonlinear chloride ion transportation equation with heterogeneous parameter should be set up. .Use of compactly supported radial basis function expansion method and the radial integration method, a meshless boundary element method should be developed to solve the constructed nonlinear transportation equation. Some interface programs should be constructed to integrate the developed meshless boundary element program with commercial finite element software, and data exchange between developed program and software could be implemented. The mutual coupling mechanism of concrete crack propagation and chloride ion transportation processes could be revealed. Under the proposed coupling mechanism, degradation of the structural resistance should be evaluated with structural reliability analysis methods. A more scientific model for evaluating the durability of concrete structures could be obtained.

氯离子侵蚀是混凝土耐久性研究中的关键问题，目前需有机结合材料学、结构学和力学等多学科交叉开展研究。以建立载荷与环境作用下混凝土结构损伤破坏与耐久性评估模型为目标，研究氯离子侵蚀混凝土的非线性过程，探索温度、干湿循环、表面氯离子浓度以及结构中裂纹的几何形态对氯离子侵蚀过程的影响机理，揭示混凝土非均匀损伤演化规律。采用离散元和扩展有限元方法，研究受荷混凝土中裂纹的萌生、动态扩展及其受粗集料随机分布和内部材料界面的影响程度，结合破坏实验，构建裂纹的时空演化模型。通过理论分析和实验观测，得到包含裂纹动态扩展影响的混凝土时变扩散系数，建立相应的氯离子输运方程。综合运用紧支径向基函数展开和边界元法，发展求解非线性输运方程的数值方法。通过裂纹模拟软件与编制程序的联合求解，建立氯离子侵蚀与混凝土开裂间的耦合关系。利用概率统计方法，评估耦合作用机制下混凝土结构的抗力退化情况，为完善混凝土耐久性评估提供基础。

以建立载荷与环境作用下混凝土结构损伤破坏与耐久性评估模型为目标，建立了混凝土中氯离子扩散问题的多尺度近场动力学模型，探索了混凝土细观参数对氯离子侵蚀过程的影响；建立了温度、干湿循环、表面氯离子浓度以及结构中裂纹的几何参数与混凝土中氯离子表观扩散系数间的定量关系，为研究氯离子侵蚀混凝土的非线性过程提供了理论基础。建立和发展了高效模拟混凝土中裂纹动态扩展过程的近场动力学模型，厘清了细观结构特征与损伤破坏模式间的关系，为深入研究混凝土损伤断裂问题奠定了基础。建立了氯离子侵蚀与混凝土锈胀致裂问题的过程耦合求解方法，探索了多筋锈胀导致混凝土开裂破坏的机理，研究了海洋环境下三维钢筋混凝土梁、柱的耐久性破坏过程，结果表明箍筋数量及分布方式对混凝土结构的开裂破坏模式影响显著。综合氯离子非线性扩散分析方法、混凝土多尺度破坏模拟技术，以及过程耦合求解技术，建立和发展了载荷与环境作用下氯离子侵蚀与混凝土开裂过程耦合分析方法，模拟分析了荷载与干湿循环共同作用下氯离子侵蚀混凝土的非线性过程，发现了干湿循环过程中干燥与湿润曲线具有显著拐点和交叉点的有趣现象。对于上述发展的氯离子扩散问题的多尺度近场动力学方法、混凝土细观损伤破坏问题的近场动力学方法分别编制了MATLAB程序；对于氯离子侵蚀与混凝土锈胀破坏问题的耦合求解技术，编制了基于ABAQUS软件的接口程序。以上成果为科学评估混凝土结构的耐久性问题奠定了重要基础。