湿热环境下预应力CFRP加固RC梁的疲劳损伤演化及刚度退化模型研究

Hygrothermal exposure, overloading and heavy traffic can cause durability problem of RC beams strengthened with pre-stressed CFRP. To reveal the fatigue damage evolution law and flexural stiffness deterioration mechanism of RC beam strengthened with pre-stressed CFRP, this project is planning to study the anchorage system of pre-stressed CFRP plates and bond interface of CFRP-concrete. To reveal the damage evolution law of pre-stressed CFRP anchorage system and develop a time-dependent bond-slip model with anchoring, hygrothermal exposure accelerating and overloading fatigue tests will be conducted, as well as mesoscopic and chemical analyzing the anchored parts. To reveal the CFRP-concrete interface bond deterioration, meanwhile, non-destructive technique based on piezoelectric ceramics will be applied to monitor the interface properties while the specimens exposed to natural environment are under sustained loading. For different sizes of specimens, thereafter, a fatigue test will be conducted to understand the size effect of pre-stress loss, and to develop a fatigue cumulative damage model based on stiffness degradation. Finally, based on the above research results, the long-term pre-stress loss evaluation method of strengthened RC beams will be proposed, and the time-dependent stochastic stiffness degradation model will be developed. The research results of this project could provide theoretical basis and experimental data for optimizing the pre-stress level and anchorage system and predicting the service life of bridges after strengthening. Besides, it can also be important reference for design and construction standards.

本项目针对湿热、超载、大交通量的使用环境下预应力CFRP加固RC梁的耐久性问题开展研究，以预应力CFRP板锚固体系和CFRP-混凝土粘结界面为主要研究对象，拟揭示预应力CFRP加固RC梁的疲劳损伤演化规律和抗弯刚度退化机理。通过湿热环境加速老化和超载疲劳试验，结合锚固部位的细观和化学分析，揭示预应力CFRP板锚固体系的损伤演化规律，建立锚固滑移时变模型；同时，进行自然环境下的长期持载试验，采用压电陶瓷无损检测技术监测界面性能，揭示CFRP-混凝土界面粘结性能退化规律；其后，对不同尺度构件进行疲劳试验研究，探讨预应力损失的尺寸效应，建立刚度下降疲劳累积损失模型；最后，基于上述研究结果，提出加固RC梁长期预应力损失评估方法，建立基于时变可靠度的刚度退化模型。本项目的研究成果将为优化预应力水平和锚固体系、为预测加固桥梁的使用寿命提供理论依据和实验数据，为相关设计和施工规范提供重要参考。

预应力碳纤维增强复合材料（CFRP）加固作为一种主动加固技术，能抑制裂缝开展，有效地提高RC桥梁刚度。然而南方沿海地区湿热环境对锚固系统和CFRP-混凝土界面的侵蚀，将导致长期预应力损失和CFRP加固效率降低，使桥梁的刚度不足以及裂缝进一步开展，从而严重影响预应力加固结构的耐久性能。本项目考虑湿热环境和过载疲劳损伤的影响，对 CFRP-混凝土界面以及预应力 CFRP 加固混凝土梁的耐久性能、裂缝开展行为和刚度退化规律开展了理论和试验研究：（1）研究预应力CFRP板加固锚具加速腐蚀下的性能退化规律，采用光纤光栅监测了锚具试件在电解失重过程中的预应力损失，探讨了锚具滑移的变化规律和腐蚀后的承载能力，结果发现夹片锚具腐蚀后的预应力损失小、锚固效率无明显降低，具有很好的耐久性。（2）开展CFRP-混凝土界面力学性能研究，揭示了过载疲劳损伤和湿热环境作用下CFRP-混凝土界面破坏机制，并构建了界面粘结滑移本构模型；采用压电陶瓷（PZT）的压电阻抗（EMI）技术对过载疲劳损伤和湿热环境作用CFRP-混凝土界面的粘结性能退化规律进行研究，实现了无应力状态下界面性能长期监测，比应变片能更有效地表征荷载作用下界面的性能退化和损伤发展过程。（3）对不同环境、不同预应力水平和不同持载水平的预应力加固梁进行长期持载研究，结果表明预应力加固梁的锚固系统未受持载和环境的影响，而粘结层在潮湿环境下有一定的退化，并给出了承载力和长期预应力损伤的评估方法。（4）探索了预应力加固的尺寸效应，发现胶层粘结对足尺梁的抗弯性能和破坏模式有明显影响；基于裂缝间的剪应力分布规律，构建了湿热环境下预应力 CFRP 加固混凝土梁的平均裂缝间距计算模型；并基于本文获得的湿热环境下粘结滑移本构构建了刚度预测理论模型。本项目的研究成果将为优化预应力水平和锚固体系、为预测加固桥梁的使用寿命提供理论依据和实验数据，为相关设计和施工规范提供重要参考。