大跨度悬索桥施工过程中主缆二次应力实测研究

Field measurement on secondary stress of main cable of long-span suspension bridge in the process of construction

悬索桥主缆钢丝的实际应力关系到主缆的安全储备,为研究大跨度悬索桥施工过程及成桥时主缆断面的应力状态,对南京长江四桥加劲梁吊装过程中桥塔索鞍附近主缆断面的应力进行了现场实测。实测结果表明主缆断面的二次应力主要由钢丝的不均匀轴向应力组成,主缆二次应力随着施工进程在嵌固端处逐渐积累,且变化趋势与主缆在索鞍处的转角变化一致。根据测试数据建立主缆二次应力的拟合曲线,以此来计算个别无测试数据工况的断面二次应力,最终得到南京长江四桥施工全过程的主缆断面二次应力变化曲线。在成桥状态时,桥塔索鞍两侧出口处主缆的二次应力最大,分别为171MPa、136MPa,与平均轴向应力之比为0.26、0.21。研究成果可为大跨度悬索桥主缆的设计及安全储备的确定提供有价值的参考。

The real stress of strand wires related to safety reserve of main cable. To study the stress state of main cable of long-span suspension bridge during construction process and in the finished bridge state, the stress of main cable is measured on site for several sections which are near pylon saddle during stiffening girder lifting process of Nanjing Yangtze River Fourth Bridge. The results show that secondary stress is mainly composed by non-uniform axial stress. Secondary stress accumulates gradually in the fixed-end with construction process, and its tendency is consistent with rotation angle change of main cable at the pylon saddle. According to the test data, secondary stress formula with rotation angle is fitted, and secondary stress is calculated by the fitting formula for a small amount of construction cases in which there is no test data. Finally, the variation curve of secondary stress of main cable is obtained for whole construction process of Nanjing Yangtze River Fourth Bridge. The maximum secondary stress of main cable at both sides outlet of pylon saddle is 171MPa and 136MPa respectively in the finished bridge state. Ratio of secondary stress to average axial stress is 0.26 and O. 21 respectively. The research can provide valuable reference for design and determining safety reserve of main cable of long-span suspension bridge.