【作者】 陈妤；

【导师】 刘荣桂；

【作者基本信息】 江苏大学 ， 固体力学， 2011， 博士

【摘要】 现代预应力混凝土结构以其良好的结构性能、经济节能的社会效益,成为工程应用最为广泛和最具潜力的一种结构。在长期恶劣侵蚀环境作用下,该结构会出现内部损伤、甚至承载性能与使用功能退化等耐久性问题。目前,国内外对多种侵蚀环境作用下预应力混凝土结构耐久性能研究相对较少。本文结合国家自然科学基金资助项目“双指标侵蚀环境作用下预应力结构耐久性试验与寿命预测研究(项目编号：50878098)”,通过试验分析与理论研究,探索氯盐侵蚀与冻融循环对预应力混凝土构件抗弯性能的影响与劣化规律。主要完成了以下工作：(1)完成了氯盐与冻融循环作用条件下预应力混凝土构件耐久性试验。通过对20根预应力混凝土构件进行正交侵蚀试验(先冻融后氯盐侵蚀,先氯盐侵蚀后冻融,冻融与氯盐侵蚀同时进行),找出最不利侵蚀工况；利用相对动弹性模量的衰减规律,分析了构件的损伤失效过程,测试不同侵蚀工况下氯离子含量,并对构件进行承载力试验,研究冻融循环与氯盐侵蚀作用下预应力混凝土梁的承载性能退化规律。(2)建立了考虑氯盐与冻融循环耦合作用下预应力混凝土中氯离子二维扩散齐次模型。针对无限大的扩散介质,以综合正负峰值温度差、氯离子扩散系数的时间依赖性和环境温湿度等影响的实际预应力混凝土氯离子方程为基础,分别在常数边界条件和幂函数边界条件下,推导出二维氯离子扩散理论的齐次模型,且探讨了水胶比、应力水平与龄期等对预应力混凝土结构氯离子扩散的影响。(3)对冻融循环与氯盐侵蚀条件下的预应力混凝土梁抗弯性能退化规律进行数值模拟。通过有限元方法,对不同腐蚀工况条件下的预应力混凝土梁承载力退化规律进行模拟,探讨了腐蚀条件对承载性能的影响；根据耐久性试验与数值模拟进行对比,拟合得出冻融循环与氯盐侵蚀耦合作用下预应力混凝土梁开裂荷载退化系数。(4)提出了冻融条件下预应力混凝土结构氯盐侵蚀的可靠度分析模型。针对季节性冰冻地区的海工结构耐久性失效特点以及结构耐久性具体要求,从失效率与可靠度的关系入手,运用随机场理论,综合考虑正负峰值温度差、氯离子临界浓度与预应力的影响,提出了冻融条件下预应力结构氯盐侵蚀的可靠度分析模型。通过算例,讨论了离散数目对失效概率的影响,并对氯离子浓度、保护层厚度等相关随机变量进行了灵敏度分析。(5)基于可靠度理论与Monte Carlo法对混凝土结构(RC/PC)进行了耐久性评估与寿命预测。考虑耐久性寿命预测中的不确定性因素,将影响耐久性寿命的参数作为随机变量,以现场实测数据推算出的结构耐久性参数为基准,确定了各参数的随机分布,建立了包括多个随机变量的概率型耐久性寿命预测模型。此外,对随机模拟产生的假设参数及预测参数的概率分布特征、统计分布参数及其灵敏度等进行了分析,得到了寿命预测模型中假设参数的变化对预测结果的影响程度。研究结果表明：预应力水平对混凝土构件在冻融循环与氯盐侵蚀过程中相对动弹性模量的变化起着重要的影响,预压应力的存在抵消了一部分冻胀压力,延缓了混凝土内部裂缝的开展。本文主要研究内容为相关混凝土设计规范的修改与完善提供一定参考。更多还原

【Abstract】 With good performance and energy-efficient social economy, modern prestressed concrete (PC) structures is one of the most extensive and potential structures. In the condition of long harsh corrosion, there are a series of durability problems, such as internal damage and even degradation of bearing behavior and service performance. At home and abroad, durability research on prestressed concrete structures under various erosion environment is relatively few. Combining with the National Natural Science Foundation of China, " Research on durability test and life prediction of prestressed structure under double index erosion environment"(NO:50878098), the paper has explored the influence and deteriorating law to flexural performance of PC members under freeze-thaw cycle and chloride attack, based on test analysis and theory research. the following are main achievements:(1) Durability test of prestressed concrete members under freeze-thaw cycle and chloride attack is finished. Based on orthogonal erosion test on 20 PC specimens (freeze-thaw to chloride attack, chloride attack to freeze-thaw and freeze-thaw and chloride attack at the same time), the most unfavorable condition is found out. The damage failure process of prestressed concrete member is analyzed by attenuation law of relative dynamic elastic modulus. Chloride content under different erosion conditions is measured. Then, bearing capacity deteriorating law of PC beam under freeze-thaw cycle and chloride attack is discussed by bearing capacity experiment.(2) Two-dimensional chloride ion diffusion homogeneous model in prestressed concrete considering freeze-thaw cycle and chloride attack is modeled. According to infinite spread medium, based on integrated positive and negative peak temperature difference, chloride diffusion coefficient of time dependence and the influence of temperature and humidity, two-dimensional homogeneous chloride diffusion model is deduced, under both constant boundary conditions and power function ones. The influence of water-binder ratio, stress level and age on chloride diffusion is discussed.(3) Deteriorating law of flexural performance for PC members under freeze-thaw cycle and chloride attack is simulated. With simulating the bearing capacity deteriorating law of PC beam under different corrosion conditions by finite element, the influence of corrosion condition on bearing capacity is discussed. Based on the comparison between durability test and numerical simulation, the cracking load degradation coefficient in PC beam under freeze-thaw cycle and chloride attack is fitted.(4) Reliability analysis model of PC beam with chloride attack and freeze-thaw cycle is put forward. Focusing on durability failure of prestressed marine structures and requirements on structural durability in seasonal ice regions, reliability analysis model of PC beam under chloride attack and freeze-thaw cycle is put forward by stochastic field theory, considering the influence of positive and negative peak temperature difference, chloride critical concentration and prestressing. It is discussed on the influence of discrete number on failure probability, and sensitivity analysis of chloride concentration, cover thickness and other correlated variables.(5) Durability assessment and life prediction of concrete structures (PC/RC) based on fuzzy reliability theory and Monte Carlo method. Considering uncertainty factors in durability life prediction, random distributions of various parameters are determined, taking the affecting parameters as random variables. According to the structure durability parameter calculated from actual measurement, probabilistic durability life prediction model including multi-random variables is established. Moreover, the probability distribution, statistical distribution parameters and sensibility of hypothesis parameters produced by random simulation is analyzed. The influence of hypothesis parameters variation on the prediction results is discussed.It is shown that, during the process of freeze-thaw cycle and chloride attack, prestress level plays an important role to variation of relative dynamic elastic modulus. The prestressing will offset a part of frost-heaving force, delaying crack development inside concrete, which provide reference for modification and perfection of related concrete design code.更多还原