【作者】 刘欣；

【导师】 别社安；

【作者基本信息】 天津大学 ， 水利工程， 2012， 硕士

【摘要】 钢筋混凝土结构是当今主要结构形式，它广泛地应用于港口和海洋工程中。在氯盐侵蚀环境下，随着使用时间的增长，大量的钢筋混凝土结构出现耐久性破坏。因此，对氯离子侵蚀环境下钢筋混凝土构件寿命进行预测成为钢筋混凝土耐久性设计和评估等急需解决的问题。然而实际工程中，荷载作用下的大部分混凝土结构都是带裂缝工作的，裂缝的出现又加剧了耐久性问题。据此，本文针对耐久性问题最为突出的氯盐环境中混凝土结构，建立恒定荷载与氯盐侵蚀耦合作用下钢筋混凝土耐久性寿命预测模型。首先，介绍了完整混凝土中传统的氯离子扩散模型并分析了模型中各参数的影响因素和统计特征。在此基础上采用抽样模拟的方法分析钢筋初锈时间的统计特征，发现其服从对数正态分布；通过对影响钢筋初锈时间的各参数进行灵敏度分析，发现表面氯离子浓度、临界氯离子浓度和保护层厚度对初锈时间影响显著。其次，分别建立了荷载-裂缝模型和裂缝-氯盐侵蚀模型。模型考虑了单一最大裂缝宽度对氯离子扩散系数的影响；此外还考虑了氯离子扩散系数随时间衰减的特性以及裂缝宽度随时间增长而逐渐增大的趋势。本文采用MATLAB软件建立基于有限差分法的二维氯离子扩散模型。然后，针对本文建立的荷载-氯盐侵蚀耦合作用模型对一工程实例进行计算，结果表明：氯离子在裂缝附近扩散较快，离裂缝较远的地方扩散近似为一维扩散；氯离子扩散系数随时间衰减的特性对氯离子的扩散影响显著。根据灵敏度分析结果发现：为了提高混凝土构件的使用寿命，可以考虑首先降低混凝土的水胶比，其次提高混凝土保护层厚度。最后，采用概率性方法即Monte-Carlo抽样法模拟开裂混凝土构件的失效概率随时间的变化。研究结果表明：保护层厚度对开裂混凝土耐久寿命的影响显著。本文还将概率性方法的计算结果与确定性方法作对比，发现基于确定性方法得到的耐久寿命明显大于基于概率性分析方法计算得到的结果，概率性方法的结果更偏于保守。本文基于传统扩散方程，建立了荷载-氯盐侵蚀耦合作用耐久寿命预测模型。所得成果能为海洋环境中混凝土结构耐久性设计提供理论依据。更多还原

【Abstract】 As the main structure forms nowadays, reinforced concrete structure has beenwidely used in harbor and marine engineering. With the growing of using time, alarge amount of reinforced concrete structures face durability damage under chlorinesalt erosion. As a result, service life prediction for reinforced concrete structuresunder chlorine salt erosion is a crucial problem to solve for durability and designevaluation. Besides, in actual engineering, most reinforced concrete structures underload work with crack, and the crack intensifies durability problems. Hereby,according to the most obvious problem of reinforced concrete structure under chlorinesalt erosion among durability problems, the paper builds prediction model for durablelife of reinforced concrete structures under the coupling action of constant load andchlorine salt erosion.First, the paper introduces traditional chloride’s diffusion model in concrete, andsummarizes influencing factors and statistical characteristics of the parameters. On thebasis of this, analysis of the statistical characteristics of initial corrosion time ofreinforcing bar is done with sampling simulation method, and it is found that theyfollow lognormal distribution. The paper finds that surface chloride concentration,critical chloride concentration and cover thickness have significant effect on initialcorrosion time by analyzing sensitivity of the parameters which influence initialcorrosion time.Second, the load and crack width model and the crack width and chlorine salterosion model are built. The models consider the impact of single maximum crackwidth on chlorine diffusion coefficient, the reducing of chlorine diffusion coefficientwith time and the growth of crack width with time. The paper builds2-D chlorinediffusion models with finite differential equations.Third, calculation of an actual project is done with the model of coupling actionof load and chlorine salt erosion. According to the results, chloride ion defuses fasteraround crack and it is better approximated as one-dimensional diffusion far to thecrack. The characteristic, that chloride diffusion coefficient reduces with time, hassignificant impact on diffusion of chloride ion. As is shown in the analysis results ofsensitivity, in order to increase service life, we should think first about the reductionof concrete W/C, and improving concrete cover thickness next. Finally, the paper simulates the change of failure probability with time by usingprobabilistic method——Monte Carlo sampling method. The results show that thecover thickness has great effect on the failure probability of concrete members.Besides, the paper makes comparison of the results of probabilistic method and that ofdeterministic method, and it is found that the latter results are greater that the formerones. So the results of probabilistic method are more conservative.The paper is based on traditional diffusion equation, and builds prediction modelfor durable life of reinforced concrete structures under the coupling action of load andchlorine salt erosion, the results of which can provide theoretical basis for durabilitydesign of concrete structures in marine environment.更多还原