大件运输车载下考虑强度退化过程的钢绞线斜拉索安全评估

Safety Assessment of Steel Strand Stay Cable Under Customized Transport Vehicle Load Considering Strength Degradation

为实现大件运输车载下退化钢绞线斜拉索安全评估,首先,在总结已有研究成果的基础上建立了"微动-腐蚀-疲劳"损伤历程下的钢绞线斜拉索强度退化模拟方法;其次,根据斜拉索运营阶段安全性的内涵,依据可靠度理论建立了大件运输车载下的两层次安全评估方法,两层次安全评估极限状态分别对应于不满足规范要求安全储备的状态及拉索断裂破坏,明确了两层次安全评估目标可靠指标的确定方法;最后,以一个实例分析对所构建的钢绞线斜拉索强度退化模拟方法及两层次安全评估方法的应用进行说明。结果发现:采用所构建的模拟方法可顺利实现对钢绞线斜拉索强度退化过程的模拟,钢绞线斜拉索在腐蚀过程开始之前,其抗拉强度会在微动磨损进程下损失约5%,一般大气环境下,服役30年时抗拉强度退化至初始水平的约72.6%;第1层次安全评估目标可靠指标可选择为3.09,第2层次安全评估目标可靠指标的确定应同时考虑正常运营荷载及年均大件运输车辆授权通行次数的影响;考虑到大件运输车辆通过大跨桥梁时严格交通管制的艰难程度,安全评估过程应考虑正常交通荷载的影响,考虑一般运行状态或密集运行状态活载模型对安全评估结果的影响较小。所建立的两层次安全评估方法可为大件运输车载下大跨桥梁关键构件安全评估提供参考。

The strength degradation simulation method of steel strand stay cable within the damage process of "fretting-corrosion-fatigue"was established based on existing research to realize its safety assessment under the load of a customized transport vehicle(CTV).The duallevel safety assessment method under the CTV load was established,according to the implications of operational safety of stay cable,in which the two limit states corresponding to the condition that the safety cannot satisfy the code requirement and the condition of brittle failure.The determination method of the target reliability index of the dual-level safety assessment was also proposed.Finally,the applications of the simulation method of strength degradation of steel strand stay cable and the dual-level safety assessment method were illustrated through a case study.The results show that the strength degradation procedure of the steel strand stay cable can be successfully simulated by the proposed method.The tensile strength decreases by 5% under the fretting wear process before the corrosion process,and the tensile strength decreases to72.6% of the original value over a 30-years service period.The target reliability index of the first-level safety assessment is suggested to be 3.09.The determination of the value of the second-level assessment should consider the influence of normal operation load and the average annual frequency of CTV authorization.Considering the difficulty of controlling the passage of a CTV over a long-span bridge,the safety assessment should include the impact of the load of normal traffic.Additionally,the live load model based on general or dense operating states has little influence on the assessment result.The proposed dual-level safety assessment method can be used as a point of reference for the assessment of the safety of key components of long-span bridges under CTV load.