表层嵌贴预应力FRP加固混凝土结构的疲劳损伤机理和寿命评估方法研究

While the technique of strengthening reinforced concrete structures with prestressed near surface mounted (NSM) fiber reinforced polymer (FRP) has shown significant advantages, including full utilization of performance of FRP materials, significant improvement of performance of strengthened structures, and saving of strengthening costs, the related research is still in its beginning stage, and study on fatigue behavior of the strengthened structure is lack, which limits the application of the technique in bridges and other structures under cyclic loading. This project aims to study the damage accumulation mechanism and fatigue life assessment method of reinforced concrete structures strengthened with prestressed NSM FRP. To achieve this goal, the softening of slip module and propagation of debonding crack of the interface between the FRP and concrete under fatigue load will be investigated through the tests and analysis of the bonded joint. On this basis, the project will establish the damage accumulation mechanism and the model of degradation of interfacial bond between the NSM FRP and concrete under fatigue load. Furthermore, the beam tests will be conducted to study the failure modes and the damage accumulation mechanism of the strengthened beam under fatigue load, and thus the key factors of every failure mode will be determined. The Fracture Mechanical Method based on the constraint stress area will be developed to establish the model of fatigue crack growth rate of the strengthened structures. The model of analyzing the load-carrying behavior of the NSM FRP strengthened structures with fatigue damages and the identification method of the failure mode under fatigue load will be developed. Finally, the method of assessing the fatigue life of reinforced concrete structures strengthened with prestressed NSM FRP under fatigue load will be established. The application of this project will provide experimental and theoretical evidence for long-term behavior assessment and design of the reinforced concrete structures strengthened with prestressing FRP, and it is essential to the research of theory of fatigue damage of reinforced concrete structures.

表层嵌贴（NSM）预应力FRP加固钢筋混凝土结构具有材料性能利用充分、结构性能提高显著、及加固成本低等优势，但研究尚处于起步阶段，疲劳性能研究非常匮乏，限制了其在桥梁等工程结构中的应用发展。本项目以预应力NSM FRP加固钢筋混凝土结构的疲劳寿命评估为目标，从粘结界面的层面考察疲劳荷载下粘结滑移模量退化及剥离裂缝扩展规律，明确NSM FRP-混凝土粘结界面的疲劳损伤机理及退化模型；通过构件试验探明加固结构的破坏模式及损伤机理，确定特定损伤破坏类型的关键影响因素；发展基于约束应力区的断裂力学方法，建立加固结构损伤扩展速率模型；构建基于疲劳损伤分析的加固结构性能分析模型和破坏模式判别方法，明确疲劳失效准则，建立预应力NSM FRP加固混凝土结构的疲劳寿命评估方法。本项目将为预应力FRP加固钢筋混凝土结构的长期性能设计与评估提供试验与理论依据，并对混凝土结构疲劳损伤理论研究具有重要意义。

表层嵌贴预应力FRP是一种新兴混凝土结构加固技术，其具有加固成本低、加固效果突出、加固耐久性好等显著优势，正在成为FRP加固技术领域的重要研究方向。然而目前关于嵌贴预应力FRP加固技术的研究主要集中于加固结构的静力性能方面，对于疲劳荷载下应用该技术加固的结构其受力性能、破坏行为和疲劳寿命评估方法等关键科学问题的研究非常有限。本项目首先从材料粘结层面出发，考察了静力与疲劳等荷载因素、混凝土强度与槽尺寸等构件参数、冻融等环境因素下FRP与混凝土界面的粘结性能，分析了因素耦合作用下粘结界面的退化行为和损伤机理，明确了FRP与混凝土界面剥离这一关键破坏模式对应的疲劳极限，建立了多因素影响下的嵌贴FRP-混凝土粘结滑移关系模型和疲劳寿命预测模型；进一步的，研究了静力与疲劳荷载下表层嵌贴预应力FRP加固钢筋混凝土梁的受力性能，明确了加固构件的主要破坏模式及其对应损伤机理，确定了特定损伤破坏类型对应的关键影响因素临界阈值，提出了加固构件疲劳损伤与寿命评估方法；另外，对于表层嵌贴预应力FRP加固钢筋混凝土梁易发生粘结端部剥离破坏从而显著削弱构件整体承载能力的特点，针对性的提出了设端部无预应力段和梯度预应力段等两种表层嵌贴预应力FRP粘结端部构造措施，开展静力与疲劳试验研究了构造的传力行为与机理，明确了构造措施的突出效果。本项目从材料粘结、构件受力及构造措施等不同层面开展了疲劳荷载下表层嵌贴预应力FRP加固混凝土结构的试验研究，成果获得的试验数据和重要科学理论具有重要意义，填补了嵌贴预应力FRP加固混凝土结构疲劳性能评估与设计的知识空缺，解决了加固结构疲劳破坏模式和损伤机理等若干关键科学问题，并为科研人员后续研究工作奠定了坚实基础。