基于吊索瞬断动力过程的自锚式悬索桥结构易损性定量评估研究

The bridge catastrophic event caused by cable damage or fracture always has great unexpectedness and heavy destructiveness. However, the research on vulnerability of bridge structures based on hanger damage or fracture conditions is heavily scarce yet. Taking self anchored suspension bridges as the object, the research is carried out by using the theoretical analysis, methods of numerical simulation and model test. The influence mechanism to the mechanical behavior and the internal force redistribution mechanism of the bridge on different hanger damaged conditions will be ascertained. The simulation method of hangers fractured on the same time or foot by foot is established to reveal the mechanical behaviors and dynamic evolution characteristics of the structural response in this dynamical course. The topological characteristics and destroy path of hangers are determined. The amplification effect and its differences of structural response are obtained. According to these above, the sensitivity of key mechanical index of the structure to each hanger damage and fracture conditions is analyzed. The selection method of hanger damage or fracture scenario is put forward and the quantitative evaluation parameters and evaluation indicators are determined. Then, the vulnerability evaluation framework of the bridge structure is established and the vulnerability of self anchored suspension bridges on the of hanger damage or fracture is quantitatively evaluated. The outcome of this research is useful to improve the design theory of cable system of self anchored suspension bridges and can provide scientific basis to the disaster prevention and mitigation of cable supported bridges. It has important scientific significance and engineering value.

因吊索损伤、破断引发的桥梁灾变突发性强、危害性大，而目前针对吊索损、断条件下的桥梁结构易损性量化评估研究极为匮乏。本项目以自锚式悬索桥为研究对象，通过理论分析、数值模拟及模型试验相结合的方法，深入研究吊索损伤对结构受力性能的影响机理及结构内力重分布制；建立吊索单索/多索渐次破断动力过程数值模拟方法，研究吊索破断后自锚式悬索桥结构动力响应过程力学行为特征及动态演变规律，探明吊索系统拓扑特性及渐次破坏路径，明晰结构响应动力放大作用规律及差异特征，以此为基础，研究结构关键力学指标对吊索不同损、断工况的敏感性，提出吊索损伤场景选取准则，明确结构性能量化评价参数和损伤分级评定指标，进而构建合理的评估框架，对自锚式悬索桥在吊索损伤、破断条件下的结构易损性做出定量评价。研究成果有助于进一步完善自锚式悬索桥缆索系统设计理论，同时可为缆索承重桥梁防灾、减灾工作提供科学依据，具有重要的理论意义及工程实用价值。

项目以自锚式悬索桥为研究对象，以断索动力过程自锚式悬索桥结构易损性的定量分析为研究重点，制作了某自锚式悬索桥的数值模型和缩尺模型，分析了吊索损伤对桥梁静力性能的影响，探索了吊索破断后桥梁结构的动态力学响应变化，提出了基于吊索破断动力过程的自锚式悬索桥结构易损性评估方法。.（1）对不同吊索损伤工况下桥梁结构性能进行静力分析，结果表明：吊索损伤后吊索系统进行拉力重分布，而主梁和主缆线型的变化很小；吊索发生损伤后与其同侧相邻两根吊索静拉力的增加量占其拉力减少量的84.08%以上，拉力重分布主要发生在损伤吊索及其紧邻两根吊索之间；两根吊索发生损伤引起同侧吊索静拉力的重新分布，与这两根吊索分别损伤引起同侧吊索静拉力重分布的叠加效果几乎是等效的，误差小于5%；.（2）结合缩尺模型试验与数值模拟，对不同断索工况下桥梁结构的力学响应进行静力和动力分析。结果表明：各断索工况下，与破断吊索相邻吊索的动力放大系数DAF最大可达1.75与2.46之间，断索对桥梁结构的动力冲击效应显著；断索同样仅对与其同侧紧邻吊索的拉力及其下部主梁的竖向弯矩有较大影响，而对主梁挠度和主缆拉力的影响较小；相较于单根吊索破断，相邻两根吊索破断后结构的力学响应更为剧烈(DAF可达2.27，DCR达到0.87)，可能导致吊索发生连续破断；.（3）通过考虑吊索破断前后结构应变能的变化，提出了一种适用于自锚式悬索桥结构的易损性定量评估方法。以某主跨160m的自锚式悬索桥为例，对易损性定量评估方法进行应用。结果表明：L1#和L28#吊索分别为该自锚式悬索桥的边跨和中跨的最重要吊索；单根吊索瞬时破断后悬索桥冗余度均大于2，此时桥梁整体的易损性较小；L28#、L27#吊索破断后桥梁冗余度降为1.534，而L29#吊索的冗余度已降为1.346，说明两根吊索发生相继破断时虽然悬索桥易损性仍较大，但吊索的冗余度已达较小的程度；发生四根吊索破断时，剩余吊索冗余度的最小值小于1，说明该吊索已经屈服甚至断裂，进而引起更多吊索断裂，最终造成桥梁倒塌。