氯盐环境下混凝土结构服役寿命的可靠度随机边界元法评估

Corrosion of reinforcing steel in concrete has become a major problem world-wide, especially for such structures as bridges, parking decks, tunnels, offshore structures and other buildings exposed to chloride environments due to seawater or de-icing salts. As a result, the repair costs nowadays constitute a major part of the current spending on infrastructure, and its' service life beyond its design target obviously. Therefore, it is very necessary to research the evaluation theory and method for service life of concrete structures as a scientific and engineering problem. .In most of the current methods for service life prediction of concrete structures in a chloride environment, the chloride diffusion are described by certainty model, or the chloride diffusion coefficient and the surface chloride concentration are treated as random variables. The impacts of the random spatial distributions of chloride diffusion coefficient and the surface chloride concentration on the service life of concrete structures are not considered in these methods, and it is the reason that the service life predicted by these methods is markedly different from that of the actual structure. Considering the random spatial distributions of chloride diffusion coefficient and the surface chloride concentration, and based on the spatial randomness discretization, a stochastic boundary element method (SBEM) for two-dimensional diffusion of chloride in concrete structures is proposed by the combination of the experimental study, theory models and numerical simulation methods in this project. According to the SBEM, A reliability approach for service life of concrete structures in a chloride environment based on SBEM is established for the calculation of reliability index by use of the reliability theory. The method offers a new theoretical foundation for the service life prediction of concrete structures in a chloride environment.

氯盐环境下混凝土结构存在严重腐蚀问题，往往远低于设计使用年限就需要花巨资维护和加固，严重的甚至需要拆除重建，造成巨大的经济损失和资源浪费。.采用确定性模型常常导致高估混凝土结构服役寿命，基于可靠度分析的随机数值方法评估混凝土结构的耐久性，能够合理考虑并准确分析结构、材料及环境中各类不确定性因素对混凝土结构服役寿命的影响。但传统的不确定性分析模型中仅用随机变量来表现材料扩散参数和环境作用参数的随机性，没有考虑其空间分布的不确定性，难以准确预测混凝土结构的服役寿命。本项目拟结合模型试验、理论分析和数值模拟，揭示氯离子在含损伤混凝土结构中的时变扩散机理，建立混凝土的表面氯离子浓度、氯离子扩散系数等随机参数的空间概率分布模型，基于随机场离散理论建立混凝土结构中氯离子扩散分析的随机边界元法，并引入可靠度理论，构建氯盐环境下混凝土结构服役寿命评估的可靠度随机边界元方法。

本项目围绕氯盐环境下混凝土结构服役寿命的可靠度随机边界元法评估开展研究。在氯离子扩散系数和混凝土表面氯离子浓度的空间概率分布模型、基于随机场离散理论的混凝土结构中氯离子二维扩散的随机边界元法、氯盐环境下混凝土结构服役寿命评估的可靠度随机边界元方法等方面取得了丰富研究成果。代表性研究成果包括：（1）研究揭示了混凝土结构氯离子扩散系数和氯离子浓度的空间分布规律，提出了识别氯盐环境下混凝土结构耐久性控制区域的方法，研究建立了混凝土氯离子扩散系数、电通量等耐久性控制参数的多因素计算模型；（2）基于混凝土结构中氯离子扩散机理，建立了混凝土中氯离子扩散分析的全时域初值推进边界元法，进而通过连续级配多边形骨料的随机投放，将混凝土中的氯离子扩散域随机离散成砂浆扩散区和骨料区，据此研究提出了基于扩散场随机离散的混凝土结构中氯离子扩散分析边界元法；（3）根据氯盐环境下混凝土结构的破坏机理，建立了混凝土结构服役寿命评估的极限状态方程，提出了氯盐环境下混凝土结构服役寿命评估的可靠度随机边界元方法，求解氯盐环境下在役混凝土结构的时变可靠指标，并进而分析了混凝土结构表层区域的开裂损伤对结构耐久性可靠指标的影响；（4）建立了氯盐扩散系数上限值与设计使用年限、混凝土保护层厚度和混凝土龄期衰减系数之间的关系，形成了海洋混凝土结构耐久性设计参数限值的确定方法和步骤，进而提出了氯盐环境下混凝土结构耐久性设计方法和基于抗氯离子侵入性能和强度指标要求的混凝土配合比设计方法，同时还建立了基于双指标健康诊断方法的混凝土结构耐久性评估体系。相关研究成果在《土木工程学报》、《水运工程》、《混凝土》等期刊上发表和录用论文10篇（EI收录3篇），申请发明专利4项，获授权发明专利3项，获授权软件著作权2项。获广西科学技术进步奖一等奖1项。培养博士生5名，硕士生14名。