预应力CFRP板无粘结加固钢梁过焊孔细节疲劳机理与寿命评估方法研究

A significant number of aged steel bridges in China are moving toward the stage of encountering fatigue damage, but the traditional strengthening methods fail to prevent the structure from further corrosion and fatigue. Currently, the main drawback of the widely developed CFRP strengthening method is that the adhesive layer is liable to be failed first under cyclic loading and is therefore unable to exploit the full potential of high strength properties of CFRP. To tackle this limitation, this project, based on systematic experimental research and theoretical analysis, focuses on the impact of the new strengthening method of applying prestressed unbonded CFRP plate on the fatigue-sensitive details of steel bridges. Firstly, fatigue tests and long-term stress relaxation test of steel girders with cope hole details are conducted to study the fatigue mechanism of the strengthened steel girders and the prestress loss characteristics of the CFRP plate. Secondly, multi-scale models including the local weld profile and the influence of prestressed CFRP plate are established, and theoretical evaluation method of crack initiation life under pre-reinforcement request is developed. Thirdly, different crack sizes introduced in sub-models with cope hole details are simulated, and the assessment method of crack propagation life based on weight function fracture mechanics is proposed. In light of the various design requirements on fatigue pre-reinforcement or post-crack reinforcement, the method for determining the correspondent CFRP pre-stress level is proposed. The research is closely related to the maintenance and safety demand of steel bridges in China. The findings can shed light on the design and specification of fatigue strengthening of steel bridges.

面对我国老龄钢桥即将来临的大规模疲劳损伤问题，传统加固方法并不能使结构抵抗进一步的腐蚀和疲劳损伤。目前广为发展的CFRP加固方法的弊病是粘贴层在循环荷载下容易最先破坏而无法充分利用CFRP的高强性能。为此，本项目基于系统的试验研究和理论分析，集中关注预应力CFRP板无粘结加固新方法对钢桥疲劳敏感细节的影响。研究分为：1）对含过焊孔细节的钢梁进行疲劳试验和长期松弛性能试验，以分别研究加固钢梁的疲劳机理和CFRP板预应力损失规律；2）建立考虑焊缝局部和CFRP板预应力影响的多尺度模型，提出基于局部应力的预加固裂纹萌生寿命评估方法；3）在含过焊孔细节局部模型引入不同尺寸裂纹进行数值研究，提出基于权函数断裂力学的裂后加固裂纹扩展寿命评估方法；4）根据疲劳预加固或裂后加固的不同设计要求，提出CFRP预应力水平的确定方法。课题研究紧密结合我国钢桥维护与安全需要，可为钢桥加固设计及规范制定提供重要参考。

本项目基于系统的试验研究、数值模拟和理论分析，研究了预应力CFRP板无粘结加固新方法对钢桥典型疲劳敏感细节的影响。开展了预应力CFRP板无粘结加固含过焊孔细节无损和有损钢梁疲劳试验，以研究加固钢梁系统的疲劳机理。建立考虑焊缝局部和CFRP板预应力影响的多尺度模型，提出基于局部应力的预加固裂纹萌生寿命评估方法。在含过焊孔细节局部模型引入不同尺寸裂纹进行数值研究，提出基于线弹性断裂力学的裂后加固裂纹扩展寿命评估方法。最终建立起采用钢桥疲劳细节预应力CFRP板无粘结预加固和裂后加固的疲劳性能评估理论框架。课题研究紧密结合我国钢桥维护与安全需要，研究成果可为钢桥加固设计及规范制定提供重要参考。