部分预应力混凝土结构是桥梁工程中最常用的一种结构形式。目前，通常认为承受疲劳荷载作用的部分预应力混凝土结构，会发生始于非预应力钢筋疲劳断裂的破坏模式。但实际上在腐蚀环境中承受疲劳荷载的部分预应力混凝土梁产生疲劳荷载裂缝后，钢绞线会在预应力孔道内空洞、水分及氯离子等因素作用下发生锈蚀，从而引起承受疲劳荷载的结构发生始于钢绞线断裂的疲劳破坏模式。因此，本文结合国家科技部的高技术研究发展计划资助项目“基于疲劳和寿命的混凝土桥梁结构设计方法”(2007AA11Z133)，对在疲劳荷载循环一定次数后钢绞线发生锈蚀的部分预应力混凝土梁疲劳性能相关的问题进行了研究与分析，论文主要内容及结论如下： (1)开展了受压混凝土抗氯离子扩散性能的试验研究，从微观角度出发提出了采用混凝土受压应变建立表征荷载作用下试件内部微裂缝开展情况的估算指标—残余比裂缝面积，分析了受压混凝土试件受力性能与抗氯离子扩散性能的关系。结果表明：压力荷载作用下混凝土试件的氯离子扩散系数与残余比裂缝面积基本满足线性关系；与普通混凝土试件相比，高强混凝土试件的残余比裂缝面积对氯离子扩散系数的影响更明显。 (2)对实际工程中钢绞线受腐蚀的部分预应力钢筋混凝土梁的疲劳破坏问题进行了模拟：在疲劳荷载循环作用一定次数后，部分预应力混凝土梁中产生疲劳裂缝，在对钢绞线进行人工加速腐蚀后再进行梁的疲劳性能试验。试验结果显示：当钢绞线发生腐蚀后，继续承受疲劳荷载作用的部分预应力钢筋混凝土梁的破坏均起源于腐蚀钢绞线的疲劳断裂；钢绞线的腐蚀率严重影响试验梁的主裂缝宽度和疲劳寿命，对试验梁的跨中挠度影响相对较小。 (3)考虑钢绞线不均匀腐蚀影响的疲劳强度折减系数，对梁疲劳破坏控制截面进行应力分析时，计入应力重分布及钢筋残余应力的影响，采用分段线性的方法并通过分别表征钢筋和混凝土疲劳损伤的钢筋有效面积与弯曲受压弹性模量对材料疲劳特性进行修正完成梁的疲劳损伤全过程进行非线性分析，提出了预测钢绞线受腐蚀的部分预应力混凝土梁疲劳寿命的计算方法。结果表明：承受高周疲劳荷载的试验梁截面应力水平较低，材料均未进入塑性变形阶段，截面抗弯刚度降低并不明显，梁的中性轴位置基本不变；通过非线性分析法计算得到的钢筋和钢绞线应力值与试验结果吻合较好；引入了钢绞线腐蚀影响的材料疲劳强度折减系数后，试验梁的疲劳寿命预测结果与试验结果误差很小。 (4)采用ANSYS软件对钢绞线受腐蚀的部分预应力钢筋混凝土梁进行静力有限元分析，并在此基础上，采用FE-SAFE软件对梁进行了疲劳数值模拟，预测梁的疲劳寿命。结果表明：考虑钢绞线腐蚀影响的疲劳强度折减系数的疲劳寿命有限元分析结果与试验结果吻合较好，验证了有限元软件对梁疲劳分析的可行性及有效性。 (5)基于疲劳累积损伤模型，考虑材料疲劳强度和临界损伤的随机性，对试验梁的可靠度进行计算；在此基础上，考虑疲劳荷载和材料性能的随机性和时变性，对实际工程中钢绞线受腐蚀的部分预应力钢筋混凝土梁进行时变可靠度分析。结果表明：钢绞线锈蚀后，梁的疲劳可靠度会迅速发生衰减，在桥梁的使用过程中必须尽量避免钢绞线发生腐蚀，在服役寿命期内做好检查和维修加固工作，以保证桥梁具有足够的可靠度。 关键词：部分预应力混凝士梁；氯离子扩散；钢绞线腐蚀；疲劳寿命；疲劳可靠性

Partially prestressed concrete (PPC) structure is one of the most common structural forms of concrete bridge. At present, it is usually considered that the fatigue failure of PPC structure is due to the fatigue fracture of the tensile reinforcement. However, after cracking by fatigue loading, the steel strands in PPC structure will be corroded by the corrosion factors, such as: gas, water, chloride ions and so on. As a result, the failure of the PPC structure will be caused by fatigue rupture of the corroded strands prematurely. Consequently, the study on the fatigue behavior of PPC beams with corroded strands is very important for the structural safety. Therefore, based on the National High Technology Research and Development Program of China (863 Program)"Design Method of Concrete Beam Structure Based on Fatigue and Life" (Grant No. 2007AA11Z133), the experimental and theoretical analysis of chloride diffusion in compressed concrete and fatigue performance of PPC beams with corroded strands are carried out. The main contents and analysis results are summarized as follows. (1)Experiments of chloride diffusion of concrete under compression loading are carried out. The calculation indicator is deduced by compressive strain for characterizing the internal micro-cracks in concrete, and then the relationship between the chloride diffusion and specific crack area is analysed. The experimental results show that there is a linear relationship between the chloride diffusion coefficient and residual specific crack area, and the effect of the increase of the chloride diffusion coefficient by compressive loading is more obvious in OC than HPC. However, compared with OC, the chloride diffusion coefficient of HPC is more sensitive to microcracking in the lateral surface. (2)After several cycles of fatigue loading applied on the partially prestressed concrete beams, artificial accelerated corrosion is applied on steel strands. And then, the fatigue flexural tests of partially prestressed concrete beams with corroded strands are carried out. Experimental results show that the initiation of fatigue failure of experimental beams is owing to the fracture of the corroded stress strands and the increase of corrosion rate has a significant effect on the fatigue performance and fatigue life of experimental beams. (3)Considered fatigue flexural compressive deformation modulus of concrete and effective area as the damage parameters for concrete and reinforcement respectively, a full-range analysis method of experiment beams that can account for the effect of steel stress redistribution and the residual strain of reinforcement is proposed, based on the stress analysis of cross-section. Because of the low stress of cross section on experiment beams under high cycle fatigue loading, the decrease of section stiffness is not obvious and the depth of neutral axis is stably while the material of the beams is still in elastic deformation stage. When the reduction factor of fatigue strength caused by nonuniformed corrosion in steel strands is 1.3, the prediction fatigue life of experiment beams is proved to be generally coincided with the experimental results. (4)Based on the static analysis of experimental beams by ANSYS software, the fatigue process is simulated by FE-SAFE finite element software and the fatigue life is calculated. Comparisons of the prediction results with the experimental results, the feasibility and validity of the simulation method are verified. (5)Based on the fatigue damage cumulative model, the reliability of experiment beam is calculated, and the time-dependent reliability of PPC beams with corroded strands in practical projects is analysed by considering the randomness and the time-variation of fatigue loading and material performance paramerters. The calculated reliability results show that the corrosion rate of steel strand has a significant effect on fatigue damage of experiment beam. After steel strands corroding by chloride attack, the fatigue reliability has an obvious reduction. So it is important for bridge inspection and repair schedule for ensuring enough reliability to avoiding the corrosion on the steel strands. Key Words: Partially prestressed concrete beam; Chloride diffusion; Corroded strand; Fatigue life; Fatigue reliability