氯盐环境PC结构中钢绞线的腐蚀疲劳损伤演化规律

发布时间：2018-03-16 04:37

本文选题：预应力混凝土结构　切入点：钢绞线　出处：《中国矿业大学》2014年硕士论文　论文类型：学位论文

【摘要】：预应力混凝土结构广泛应用于国家和城市生命线等重要工程之中，其中许多结构在其服役寿命期间会同时受到环境腐蚀作用和力学疲劳作用的共同影响，从而会使结构发生腐蚀疲劳耦合损伤乃至破坏，最终酿成极其严重的后果。为此，本文针对其中氯盐环境预应力混凝土结构中钢绞线的腐蚀疲劳损伤演化进程这一具体问题展开研究，以期为系统解决PC结构的腐蚀疲劳问题提供阶段性成果。基于力筋腐蚀疲劳损伤的声发射监测需要，首先通过试验研究了混凝土握裹钢绞线中声波传播的衰减规律以及若干混凝土状况对其衰减的影响情况，结果表明，声发射信号强度会随传播距离的增大而迅速减小（即能量、幅值、持续时间和振铃计数等声波参数的衰减率随着传播距离的增大而迅速增大）；保护层厚度和水灰比越大，声波衰减越多；孔隙水饱和度越大，声波衰减越少；同时，，在试验结果的基础上，结合理论分析建立了上述各因素影响下的声波衰减预计模型。通过疲劳耦合下钢绞线腐蚀电位的测量，并以氯离子对PC结构侵蚀机理为基础，建立了考虑疲劳应力幅影响的氯盐环境钢绞线腐蚀速率模型，并进行了模型参数的讨论。研究表明，随疲劳应力幅的增大，钢绞线的腐蚀速率也增大，影响趋势呈指数函数关系。疲劳耦合下钢绞线坑蚀特征试验研究表明：疲劳作用对预应力钢绞线的坑蚀特征有影响，具体表现为蚀坑的长度、宽度和深度均随疲劳应力幅的增大而增大；同时提出疲劳作用下蚀坑体积损伤分布特征和蚀坑力学损伤指数的分布特征，研究表明上述两种损伤均随疲劳应力幅的增大而增大。通过声发射监测仪器对腐蚀耦合下预应力钢绞线的疲劳损伤进程进行了研究，结果表明，能量、撞击数和振铃计数等声发射参数能够较好的表征钢绞线的损伤进程；通过分析上述参数，发现腐蚀程度与疲劳应力幅大小对钢绞线的疲劳损伤存在显著影响：当疲劳幅度一定时，掺盐率越大，疲劳累积损伤越多；当掺盐率一定时，疲劳应力幅越大，疲劳累积损伤越多。腐蚀疲劳损伤钢绞线的静力拉伸试验表明，钢绞线的最大承载力和极限平均应变均随着应力幅的增大和掺盐量的增大而降低。钢绞线钢丝可能出现劈裂式、杯椎式及铣刀式等三种基本断口形式以及他们的组合形式。
[Abstract]:Prestressed concrete structures are widely used in important projects such as national and urban lifelines. Many of them are affected by both environmental corrosion and mechanical fatigue during their service life. This will lead to corrosion fatigue coupling damage and even destruction of the structure, and eventually lead to extremely serious consequences. In this paper, the evolution process of corrosion fatigue damage of steel strands in prestressed concrete structures in chloride environment is studied in order to provide a periodic achievement for the systematic solution of corrosion fatigue problems of PC structures. Based on the need of acoustic emission (AE) monitoring for corrosion fatigue damage of steel bars, the attenuation law of sound wave propagation in steel strands and the influence of some concrete conditions on its attenuation are studied through experiments. The results show that, The attenuation rate of acoustic wave parameters such as energy, amplitude, duration and ringing count increases rapidly with the increase of the propagation distance, and the thickness of the protective layer and the ratio of water to cement increase with the increase of the propagation distance. The more the acoustic wave attenuation, the less the acoustic wave attenuation is, the more the pore water saturation is, the less the acoustic wave attenuation is. At the same time, based on the experimental results, the prediction model of acoustic wave attenuation under the influence of the above factors is established by combining the theoretical analysis. By measuring the corrosion potential of steel strands under fatigue coupling and on the basis of the corrosion mechanism of chloride ions on PC structure, a corrosion rate model of steel strands in chloride environment considering the effect of fatigue stress amplitude is established. The model parameters are discussed. The results show that the corrosion rate of steel strands increases with the increase of fatigue stress amplitude, and the influence trend is exponential function. The experimental study on the pit corrosion characteristics of steel strands under fatigue coupling shows that fatigue action has an effect on the pit corrosion characteristics of prestressed steel strands, and the length, width and depth of the corrosion pits increase with the increase of fatigue stress amplitude. At the same time, the distribution characteristics of volume damage and mechanical damage index of pit under fatigue action are proposed. The results show that the above two kinds of damage increase with the increase of fatigue stress amplitude. The fatigue damage process of prestressed steel strand under corrosion coupling is studied by acoustic emission monitoring instrument. The results show that the acoustic emission parameters such as energy, impact number and ringing count can better characterize the damage process of steel strand. By analyzing the above parameters, it is found that the corrosion degree and fatigue stress amplitude have significant influence on fatigue damage of steel strand: when the fatigue amplitude is constant, the fatigue cumulative damage increases with the increase of salt addition ratio, and when the salt content is constant, The greater the fatigue stress amplitude, the more fatigue cumulative damage. The static tensile test of corrosion-fatigue damaged steel strand shows that the maximum bearing capacity and ultimate average strain of steel strand decrease with the increase of stress amplitude and salt content. Cup type and milling cutter are three basic fracture forms and their combination.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU378

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