基于疲劳性能的碳纤维筋锚固系统可靠性设计理论研究

Compared with traditional materials, carbon fiber reinforced plastics (CFRP) has many merits when applied in the cables of super-long span bridges while a fatigue resistant anchorage system toward CFRP tendons is the important precondition for the application. The new-type complicate anchorage system will be studied due to its excellent overall anchoring performance. On the basis of the primary research results, the synergistic work principle between bonding part and clamping parts in anchorage system and the calculation model of limit anchorage force will be studied combining with elastic mechanical methods. Based on similarity principle, composite material mechanics, fatigue theory, fatigue tests of both of CFRP tendons and the anchorage system and also the results of long-term monitoring on the anchorage system toward CFRP tendons of the cable-stayed bridge in our university, the fatigue damage mechanism and relative rule for CFRP tendons will be studied under the loading conditions of static load on radial direction and longitudinal pull-pull fatigue load. The influences on the fatigue performance will be analyzed induced by such factors as the design parameters of the assembly parts of anchorage, the thickness of bonding materials, fatigue stress amplitude, the average level of tensile stress, et al. The fatigue failure mechanism and prediction model of fatigue life for the complicate anchorage system will be studied, and the optimum method for design parameters of anchorage system will be put forward. After that, based on the structural reliability theory, the fatigue reliability of the anchorage system toward CFRP tendons will be analyzed and the reliability design theory will be set up. The expected results will exhibit a great significance on promoting the application of FRP in the cables of super-long span bridges.

与传统缆索材料相比，碳纤维增强复合材料（CFRP）在超大跨桥梁的应用中具有诸多优势，而耐疲劳性能良好的锚固系统是此应用的重要前提。本项目以静载锚固性能较优的复合型锚固系统为研究对象，在已有研究基础上，结合弹性力学理论研究锚具组装件协同工作原理和锚具的极限锚固力计算模型；基于相似原理、复合材料力学和疲劳理论，借助筋材及其锚固系统的疲劳试验，并结合本校人行斜拉桥CFRP索锚固系统的长期监测结果，研究处于径向静载和纵向拉-拉疲劳荷载下CFRP筋的疲劳损伤机理和规律，分析CFRP筋锚具组装件的设计参数、粘结介质厚度、疲劳应力幅和平均拉应力水平等因素对疲劳性能的影响，揭示CFRP筋复合型锚固系统的疲劳失效机理，建立其疲劳寿命预测模型，优化锚固系统的设计参数；进而借助结构可靠度理论，研究CFRP筋锚固系统的疲劳可靠性，建立其疲劳可靠性设计理论。预期成果对推动FRP在超大跨桥梁缆索中的应用具有重要意义。

相对传统钢材，碳纤维复合材料（CFRP）在大跨预应力结构应用中具有显著优势。然而，CFRP筋因抗剪强度低而锚固困难，尤其是其锚固系统的锚固机理及疲劳性能的研究仍未得到足够重视。.本项目研究了直筒型粘结型锚具、内锥-直筒粘结型锚具和直筒-内锥-直筒型锚具等三种锚具的静力锚固性能，建立了锚固区应力分布的通用模型。通过参数分析得出结论：内锥长/直筒长=4:1~2:1的内锥-直筒粘结型锚具在三者中锚固性能最优；在一定范围内提高内锥角、降低粘结介质的弹性模量，或者采用递变粘结介质，均有助于优化锚固区的应力分布。此外，本项目建议Smith失效准则可用于粘结型锚固系统，提出了复合型锚固系统的锚固力计算模型。.本项目研究了CFRP筋粘结型锚具在循环荷载下的结构响应、疲劳损伤规律和机理。研究表明，当应力幅不超过锚固系统极限强度的10%时且最大应力水平不超过极限强度的50%时，循环加载会使锚固系统更加稳定；而且，在此范围内增大应力幅将使锚固系统更快达到重新稳定状态；加载频率对粘结型锚固系统锚固区的温度变化产生影响，当加载频率在10Hz以上时，增大频率会导致锚固区在加载的早期和中期产生剧烈的温度上升；锚固区的温升与结构内部损伤存在内在的联系，故温升可视为结构内部损伤严重程度的标志。.研究了CFRP筋复合型锚固系统在拉-拉循环加载中的荷载-滑移关系、能量释放率变化、残余承载力、疲劳加载后的套筒及筋材的循环次数-应变关系、疲劳失效模式、锚固区的温升等变化规律。结果表明，应力比与最大应力水平对锚固区的损伤、锚固系统的协同效应和以及系统是否能重新稳定具有重要的影响；复合型锚固系统与粘结型锚固系统的疲劳损伤机理有异，且前者具有更好的抗疲劳性。.结合小尺度现场试验与数值模拟方法，对比了CFRP长索与钢索两者应用于超大跨斜拉桥时在非线性静/动力特征上的差异和抗风性能，尤其是CFRP索等刚度替换钢索时对提高结构基频、扭转振动频率和弯扭频率比等的影响，结果显示CFRP索动力性能更优。