氯离子环境中预应力FRP加固RC受弯构件疲劳失效机理研究

The bridges in service would deteriorate due to the interaction of chloride corrosion and fatigue loading in the coastal areas. Thus, it has an important guiding significance for the actual engineering project to study the failure mechanism of reinforced concrete (RC) component flexurally strengthened with prestressed fiber reinforced polymer (FRP) laminates under complex conditions. In this study, a new type of two-step corrosion test is designed for FRP-concrete joint interface, and a series of tests are conducted to measure the strain field of the FRP-concrete interface by 3D digital image correlation method. Taking account to the effect of the second corrosion, a degradation model of interface bonding is established. In addition, a series of two-step corrosion tests for RC beam strengthened with prestressed FRP are conducted. By using the technology of fiber bragg grating monitoring, the evolution of FRP prestress loss of the strengthening system in the chloride corrosion environment are studied. Based on the fatigue test of the strengthened beams after the second corrosion, the initiation and the propagation of fatigue cracks are tracked by 3D digital image correlation method and infrared detection technique, and a propagation model of the fatigue crack is established, the main parameters of which include interface fracture energy and energy release rate. Then, the relationship between the level of corrosion and fatigue damage is explored. Based on this relationship, the fatigue failure mechanism of RC beam strengthened with prestressed FRP is revealed in chloride environment, and the prediction method of the fatigue life is proposed. This study is benefit for the RC components flexurally strengthened with prestressed FRP to optimize the technological parameters and improve the reliability in the coastal areas.

沿海地区在役桥梁要经受氯离子侵蚀和疲劳荷载的共同作用，研究复杂因素作用下预应力纤维增强复合材料（FRP）片材加固钢筋混凝土（RC）受弯构件的损伤失效问题对实际工程具有重要意义。本项目设计和实施FRP－混凝土搭接界面的二次腐蚀实验，利用3D数字图像相关法测量界面应变场，建立计及二次腐蚀影响界面粘结退化模型；开展预应力FRP加固RC梁的二次腐蚀实验研究，结合光纤布拉格光栅监测技术，探索加固系统在氯离子腐蚀环境中FRP预应力的损失规律；实施加固梁二次腐蚀后疲劳实验，结合3D数字图像相关法和红外探测技术，监测疲劳裂纹萌生及扩展速率，建立以界面断裂能和能量释放率为参数的疲劳裂纹扩展模型；探索不同腐蚀等级与疲劳损伤之间的关联性，揭示氯离子环境条件下预应力FRP加固RC梁的疲劳失效机理，并提出疲劳寿命预测方法。本项目的研究有助于沿海地区预应力加固RC受弯构件工艺参数的优化和可靠性的改善。

沿海地区在役桥梁要经受氯离子侵蚀和疲劳荷载的共同作用，造成其钢筋混凝土(RC)构件长期服役后出现钢筋锈蚀、混凝土开裂和保护层剥落等损伤，导致这些结构存在一定的安全隐患。从延长桥梁结构寿命，降低维护成本的角度出发，有必要研究和发展一种既能够长期耐腐蚀、又便于施工的加固方法。近年来发展起来的预应力纤维增强复合材料(FRP)技术，它将FRP材料性能优点和预应力技术的长处结合在一起，能更好地发挥FRP片材的高强抗拉性能，是一种有前途的加固方法。然而，从现有的文献来看，国内外对预应力FRP加固腐蚀RC受弯构件的研究还相当欠缺，极大限制了该项加固技术在沿海地区中推广与应用。因此，开展氯离子环境条件下预应力FRP加固RC受弯构件疲劳失效机理的研究，既有重要的科学意义，又有实用的工程价值。. 本项目首先开展了FRP-混凝土界面组成材料在氯盐环境下的耐久性研究，包括FRP材料、环氧树脂和混凝土；设计和实施了FRP-混凝土搭接界面的二次腐蚀实验，建立计及二次腐蚀影响界面粘结退化模型；开展了预应力FRP加固RC梁的二次腐蚀实验研究，探索加固系统在氯离子腐蚀环境中FRP预应力的损失规律；实施加固梁二次腐蚀后疲劳实验，探明了界面疲劳裂纹扩展规律；探索了氯离子环境条件下预应力FRP加固RC梁的疲劳失效机理，并提出疲劳寿命预测方法。研究结果表明：FRP弹性模量随着腐蚀时间并无明显变化，然而由于浸渍树脂的水解，纤维与树脂界面出现损伤，致使FRP的抗拉强度和延伸率会随暴露时间明显下降，但其耐久性大幅优于钢材；氯离子环境会加速界面疲劳裂纹的扩展速率，界面裂纹扩展主要分为3个阶段：快速扩展、稳定扩展以及失稳扩展；氯盐环境暴露会导致加固构件疲劳破坏从混凝土层剥离向胶层剥离或FRP断裂的模式进行转变；利用本研究提出的自锚式技术，能避免加固构件的剥离破坏，同时能较好控制FRP板预应力损失，其放张后预应力损失约10%；利用本研究提出的模型能较好的预测海洋环境下预应力FRP加固RC受弯构件的承载力和疲劳寿命。

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