【作者】 李富民；

【导师】 袁迎曙；

【作者基本信息】 中国矿业大学 ， 结构工程， 2008， 博士

【摘要】 基于力筋腐蚀的预应力混凝土结构耐久性问题日益突出,但相关的研究很少。为此,该论文针对氯盐环境钢绞线预应力混凝土结构的腐蚀效应这一迫切基础问题展开研究。试验研究表明,氯盐环境混凝土内钢绞线具有典型的坑蚀形态,蚀坑几何形状可抽象为棱锥形、椭球形及马鞍形3种;蚀坑几何尺寸统计表明,坑深和坑长的分布具有分形特性,并反映了浅、短、中宽型蚀坑分布较多的特点。基于材料微观结构特征的理论分析和模拟实际条件的长期试验研究表明,氯盐环境下混凝土内钢绞线对阳极溶解型应力腐蚀和氢致开裂型应力腐蚀都不敏感;腐蚀钢绞线钢丝的弯曲疲劳试验表明,其腐蚀疲劳断裂具有典型的各项异性特征。提出了混凝土中钢筋腐蚀机理的新见解:腐蚀的阴阳极过程均主要发生在活化区,腐蚀的主要阻力只是电极的极化阻力。因此,钢筋腐蚀的控制模式包括氧扩散控制和供水条件控制2种。基于腐蚀机理新见解,根据金属腐蚀极化理论和试验测试数据及文献氧扩散系数模型,分别建立了2种控制条件下混凝土内钢筋腐蚀速率的基本理论模型和实用模型。试验结果和模型算例共同表明,正常使用时预应力结构中钢绞线的腐蚀速率比零应力时提高27%左右。静力拉伸试验表明,蚀坑导致钢绞线的脆性增加,最大承拉力和极限平均应变降低;钢绞线钢丝可能出现劈裂式、杯锥式及铣刀式等3种基本断口形式以及它们的组合形式。根据微观电镜扫描和金属断口理论并结合材料微结构特征,提出了腐蚀钢绞线钢丝基于蚀坑处珠光体团位向的微观断裂机制。根据断裂机制提出以Mises总应变作为断裂参量的腐蚀钢绞线的断裂准则。通过拉伸试验配合有限元模拟和数理统计得到腐蚀钢绞线断裂抗力的分布规律及模型;通过对4段腐蚀钢绞线的有限元模拟及数理统计得到腐蚀钢绞线断裂效应的分布规律及模型。在此基础上,借助结构可靠度理论获得了腐蚀钢绞线基于腐蚀率的断裂失效概率模型。试验研究表明,在0～0.7mm的锈胀裂缝范围内,腐蚀钢绞线与混凝土之间的粘结性能未出现明显退化,其中极限粘结强度和粘结刚度还有所提高。试验研究表明,腐蚀预应力混凝土梁发生2种典型的受弯破坏方式,一是传统的适筋破坏,另一是本文提出的断丝破坏;在腐蚀率不大(小于2.87%)的情况下,腐蚀对梁的开裂弯矩、屈服弯矩、极限弯矩、开裂挠度、屈服挠度的影响都不显著,但对极限挠度却产生了明显的影响。提出以《规范》概率极限状态设计实用表达式为依据进行腐蚀钢绞线预应力混凝土梁承载力设计和评估的方法,其中考虑腐蚀引起钢绞线抗拉强度指标概率取值的变化;在前述断裂失效概率模型的基础上,结合混凝土结构裂缝理论推导得到了预应力混凝土梁内腐蚀钢绞线的抗拉强度标准值及设计值模型。更多还原

【Abstract】 The problem of prestressed concrete structures durability based on corrosion of tendons is becoming increasingly remarkable, but the investigations are very poor. So, as the basic and instant problem, the corrosion effects of prestressed concrete structures with steel strands in chloride environment are studied in this dissertation.The experimental research shows that typical pitting forms appears on steel strands in concrete contaminated with chloride, and the configurations of pits include 3 modes as pyramid, spheroidicity and saddle. The statistics of geometrical size of pits shows a fractal characteristic in the distribution of pits depth and pits length, and there are many shallow and short and moderate wide pits.The theoretical analyse based on the microstructures of material and the long pe-riod experimental research by simulating actual conditions show that it is not susceptive to the stress corrosion cracking with both anodic dissolution and hydrogen induced cracking of steel strands in concrete contaminated with chloride. The tests indicate that the flexural fatigue fracture of steel wires of steel strands shows a typical anisotropic property.A new understanding about the corrosion mechanism of steel bars in concrete is put forward, namely, both the cathodic process and anodic process take place in active zones; polarizing resistance is the only dominant resistance of corrosion. Oxygen diffu-sion control and water supplying control are the only 2 control modes of steel bars cor-rosion.Based on the new understanding about the corrosion mechanism, the basic theo-retical models and the applied models of corrosion rate of steel bars in concrete under the 2 control conditions are derived with corrosion polarization theory and test data and oxygen diffusion coefficient from literature. Both the experimental results and the trial examples show that the corrosion rate of steel strands of prestressed structures in normal service state increases 27% than it in stress of 0.The static tension tests show that, to the steel strands with pits, the embrittlement increases and the ultimate tensile capacity and ultimate mean strain decline. The frac-tures of wires of steel strands include 3 basic modes and their combined modes, the 3 basic modes are cleavage-mode, fraise-mode and cup-mode. With SEM technique and metal fracture theory, and considering the microstructures characteristic, the mi-cro-fracture mechanism of corroded wires is put forward which based on the orientation of pearlite colonies in pits.The fracture criterion of corroded steel strands is put forward based on the fracture mechanism in which the Mises total strain is used as fracture parameter. The distribution regularities and models of fracture resistance of corroded steel strands are obtained by tensile testing cooperated with finite element simulation and mathematical statistics. The distribution regularities and models of fracture effect of corroded steel strands are obtained through finite element simulation and mathematical statistics of 4 corroded steel strands. Based on the above, the model of nonserviceable probability in fracture varying with corrosion rate is obtained through reliability theory of structures.The experimental research shows that, when corrosion cracks width is within the range of 0 to 0.7mm, the behaviors of bond between corroded steel strands and concrete do not appear significantly decreasing, and furthermore, the ultimate bond strength and stiffness increase a little.The experimental research shows that 2 typical failure modes are occurred in cor-roded prestressed concrete beams. The 2 typical failure modes include the traditional fit-reinforcement-failure mode and the wire-breakage failure mode put forward in this dissertation. Under the condition of low corrosion rate (less than 2.87%), the effects of corrosion are not remarkable to the cracking moment, the yielding moment, the ultimate moment, the cracking deflection, and the yielding deflection, but are remarkable to the ultimate deflection.It is put forward about a research idea that the design and evaluation of carrying capacity of prestressed concrete beams with corroded steel strands may be carried out in terms of the applied design expressions of probabilistic limit states used in the code, and in which the variation of probabilistic values of tensile strength indexes of steel strands caused by corrosion is considered. Based on the former model of nonserviceable prob-ability in fracture, the models of characteristic value and design value of tensile strength of corroded steel strands in prestressed concrete beams are derived by combining the crack theory of concrete structures.更多还原