海洋大气环境下预应力混凝土构件耐久性损伤相似理论研究

发布时间：2018-04-20 13:51

本文选题：海洋大气区 + 预应力混凝土结构　；参考：《江苏大学》2017年硕士论文

【摘要】：沿海地区的预应力混凝土结构物由于长期受到海水侵蚀的影响,往往会提前出现耐久性问题。外界环境的作用使它们加速了失效进程,维修或重建造成了惨痛的经济代价。因此,海洋环境下预应力混凝土结构的耐久性问题日益受到各国重视。海洋大气区是氯离子浓度较高的盐雾环境,海风等外力作用使氯离子对结构的侵蚀作用加剧,对于海洋大气区预应力混凝土构件的损伤劣化研究很有必要。本文在国家自然科学基金项目“海工预应力混凝土结构耐久性试验相似理论探索与工程应用研究(51278230)”的资助下,基于环境-时间相似理论和数值模拟的方法,探索人工气候模拟加速试验构件与连云港码头大气区横梁之间的损伤相似关系,研究海洋大气区预应力混凝土结构在钢筋锈蚀过程中混凝土的损伤问题。主要内容如下:(1)对氯离子扩散系数计算模型进行修正,考虑孔隙率、水灰比、骨料体积分数、侵蚀时间、应力状态及应力水平等因素对氯离子扩散系数的影响。在满足混凝土和易性的前提下,适当减小水灰比、增大骨料体积分数可有效降低氯离子的传输性能。对考虑和不考虑预应力损失两种情况下氯离子扩散系数计算值进行比较,探讨预应力损失对氯离子扩散系数的影响。(2)将氯离子扩散系数在构件中的分布表达式和混凝土表面氯离子浓度模型,应用到COMSOL Multiphysics有限元软件中的稀物质传递模块,对人工气候加速试验构件和连云港码头现场构件的氯离子传输过程进行模拟,所得模拟结果分别与试验和现场检测结果对比后发现,两者较为接近,由此说明数值模拟方法是可靠的。(3)利用厚壁圆筒理论,以混凝土最外边缘的环向拉应力与抗拉强度的比值定义混凝土锈胀损伤度,结合钢筋表面氯离子浓度的模拟结果,建立损伤度与钢筋腐蚀电流密度、时间的关系,从而分别确定了人工气候模拟加速试验构件和连云港码头现场构件的锈胀损伤演化方程。(4)基于环境-时间相似理论,建立人工气候加速试验构件与码头现场构件之间的损伤相似关系,得到两者之间的损伤相似常数为3.19。并总结了如何运用损伤相似关系预测混凝土保护层锈胀开裂时间。探讨混凝土保护层厚度和混凝土强度等级对混凝土锈胀损伤度的影响,增大混凝土保护层厚度和提高混凝土强度等级均能延缓保护层锈胀开裂时间,且增大混凝土保护层厚度更有效。
[Abstract]:The durability of prestressed concrete structures in coastal areas often occurs in advance due to the influence of seawater erosion for a long time. The role of the external environment has accelerated the process of failure, repair or reconstruction has a painful economic costs. Therefore, the durability of prestressed concrete structures in marine environment has been paid more and more attention. The marine large gas area is a salt fog environment with high concentration of chloride ions. The effect of external forces such as sea breeze on the structure erosion is aggravated. It is necessary to study the damage and deterioration of prestressed concrete members in marine large gas area. This paper is supported by the National Natural Science Foundation of China, "similar theory exploration and engineering application study of marine prestressed concrete structure durability test", based on the environment-time similarity theory and numerical simulation method. The damage similarity between the artificial climate simulation accelerated test member and the beam in the large gas area of Lianyungang wharf is studied. The damage of prestressed concrete structure in the process of reinforcement corrosion is studied. The main contents are as follows: (1) the model of chloride diffusion coefficient is modified to consider the influence of porosity, water-cement ratio, aggregate volume fraction, erosion time, stress state and stress level on the chloride diffusion coefficient. On the premise of satisfying concrete and ease, properly reducing the water-cement ratio and increasing the volume fraction of aggregate can effectively reduce the transport performance of chloride ions. The calculated values of chloride ion diffusion coefficient are compared with and without consideration of prestress loss. The influence of prestress loss on chloride diffusion coefficient is discussed. (2) the distribution expression of chloride diffusion coefficient in members and the chloride concentration model on concrete surface are applied to the dilute material transfer module in COMSOL Multiphysics finite element software. The chloride ion transport process of artificial climate accelerated test components and site components of Lianyungang wharf is simulated. The simulation results are compared with the test results and the field test results, and it is found that the two are close to each other. It is shown that the numerical simulation method is reliable. The thick-walled cylinder theory is used to define the corrosion damage degree of concrete based on the ratio of circumferential tensile stress to tensile strength of the outermost edge of concrete, combined with the simulation result of chloride ion concentration on the surface of steel bar. The relationship between damage degree and corrosion current density and time of steel bar is established, and the evolution equation of corrosion damage of artificial climate simulation accelerated test component and Lianyungang wharf field member is determined respectively based on environment-time similarity theory. The damage similarity relationship between artificial climate accelerated test components and dock site members is established, and the damage similarity constant between the two components is found to be 3.19. How to use the damage similarity relation to predict the cracking time of concrete cover is summarized. The influence of the thickness of concrete cover and the grade of concrete strength on the damage degree of concrete is discussed. Increasing the thickness of concrete cover and increasing the grade of strength of concrete can delay the cracking time of corrosion expansion. And it is more effective to increase the thickness of concrete cover.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU378

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