基于服役环境腐蚀的悬索桥主缆抗力退化模型和计算方法研究

With the increasing of service time, the resistance deterioration inside the main cable of suspension bridges due to the corrosion, which has seriously affected the security of bridges. Currently, the researches involve the corrosion test and corrosion mechanism of a single wire has been done. If the conclusions of these researches are used for the main cable which is composed of thousands of steel wires arranged closely, large errors will appear and it is difficult to reflect the resistance deterioration of main cable caused by the corrosion. In this study, the tests for uniform corrosion and non-uniform corrosion of the main cable under the multivarite corrosive environment are conducted, and the relationship between the time-varying function of the resistance deterioration, the amount of resistance deterioration and the corrosion state are established considering the rate changing during the corrosion. On this basis, the model and method of calculation for the main cable resistance decrease based on FEM and the conversion method between the accelerated corrosion test time and service time, involve corrosion features of rate changing,non-uniform and environmental parameters changing for the main cable in service environment. will be researched. These methods will be applied to resistance deterioration calculation of several suspension bridges. At the same time, the calculation results correctness will be verified by the accelerated corrosion tests. By the calculation and test results, the design safety factors will be assessed and the lifetime will be predicted of the main cable.

随着服役时间的增加，悬索桥的主缆内部由于腐蚀导致的抗力退化已经严重地影响到桥梁的安全。目前已经展开了针对单根钢丝的腐蚀试验和腐蚀机理研究，但若将其研究结论直接用于由上万根钢丝紧密排列而成的主缆，将产生较大误差，难以真实地体现主缆由于腐蚀导致的抗力退化问题。本研究直接以缆索为研究对象，在多因素腐蚀环境中，对其进行均匀腐蚀试验和非均匀腐蚀试验；考虑腐蚀过程中的速度变化，建立时变的抗力退化速度函数、抗力退化量与腐蚀状态之间的关系；在此基础上，针对服役环境下缆索变速度、非均匀且环境参数反复变化腐蚀的特点，研究基于有限元思路的主缆抗力退化计算模型和计算方法、加速腐蚀试验时间与服役时间之间的换算方法。将所建立的方法应用于几座悬索桥主缆的抗力退化计算中，并用加速腐蚀试验验证计算结果的正确性；通过计算结果和试验结果，对主缆进行设计安全系数评估和寿命预测。

悬索桥主缆钢丝的腐蚀严重影响着主缆的安全服役，缆内钢丝的腐蚀与其所处的缆内微环境有密切的关系，为预测悬索桥主缆内各区域中钢丝的腐蚀发展和剩余承载力，需建立主缆钢丝区域化腐蚀环境与腐蚀速率之间的计算关系。采用正交试验原理和电化学测量方法将影响钢丝腐蚀的：温度、相对湿度、NaCl浓度、pH值、钢丝拉力5个主要因素分为两组，实验得到5个因素中温度和湿度因素为主要因素，且两者相互独立，通过最小二乘法拟合得到五个因素与钢丝腐蚀速率之间的计算关系；采用中性盐雾加速腐蚀实验对镀锌和未镀锌钢丝分别进行了为期300天和150天的加速腐蚀实验，测量各个腐蚀时期内钢丝腐蚀外观，质量直径损失以及剩余承载力指标，建立了八个级别的不同腐蚀程度腐蚀外观与剩余承载力之间的对应关系。最后提出主缆分节段，截面分区域的微环境腐蚀评估方法，将实测的主缆内各区域的腐蚀环境统计为腐蚀环境年谱，并带入腐蚀速率与环境因素的计算关系，得到主缆各区域内钢丝的腐蚀速率和直径损失，其中主缆顶部区域腐蚀速率最高为0.010 8 mm/a，服役20年后直径损失约为0.02 mm即镀锌层耗损完毕，与实际桥梁检测情况吻合，服役100年直径损失将达到约1.1 mm，将不能满足主缆的设计要求。本研究建立的腐蚀速率计算方法为计算钢丝腐蚀量提供依据，得到的8级主缆腐蚀分级是指导为主缆的开缆检测评估的主要参考，最后主缆分区域的评估方法也为预测缆内钢丝腐蚀分布提供了新的思路。