悬索桥静载试验主缆索力增量测试方法

A Method for Measuring Main Cable Force Increment in Static Load Test of Suspension Bridge

主缆索力增量测试是悬索桥静载试验的主要测试项目之一,但目前悬索桥主缆索力的常用测试方法 (振动法)存在技术要求高、计算复杂等不足,无法较好地应用于桥梁静载试验中的主缆索力增量测试。因此提出一种新的、简便的主缆索力增量间接测试方法。假定主缆、主塔位于同一竖直平面内,通过分析悬索桥塔顶主缆节段受力平衡方程、主塔下横梁以上节段受力平衡方程,可以导出主缆索力与主塔下横梁以上任意截面内力之间的关系,并进一步可得到主缆索力增量与该截面内力增量的关系。根据截面的内力平衡方程及应力应变关系,得到主塔下横梁以上任意截面内力增量与其表面应变增量的关系。再根据塔柱和主缆的几何尺寸、材料特性等其他参数,即可计算出主缆索力的增量。将该方法应用到永康市溪心桥的静载试验中,进行了主缆索力增量的测试,得到了较好的效果。同时结合实例对影响主缆索力增量测试精度的各因素进行了分析,提出应变测试精度、塔柱的材料特性、测试截面面积及塔顶主缆切向与竖直向的夹角对测试结果均有较大的影响,实际使用时应对这些参数做出准确的测量或估计。该方法实施简单、方便,对仪器设备及测试条件要求较低,可为同类桥梁在静载试验中进行主缆索力增量测试提供参考。

The cable force increment test is one of the main test items of static load test for suspension bridge, but the common method of main cable force increment test （vibration method） for suspension bridge cannot be used for main cable force increment test in the static load test in a good way, because of the high technical requirements and complex computation. So a new and simple indirect testing method is proposed. Assuming that the main cable and the main pylon are in the same vertical plane, by analyzing the force balance equations of main cable segment on the top of the bridge pylon and the pylon segment above lower cross beam, the correlation equation between main cable force and the internal force of any pylon section above lower cross beam can be derived, and the correlation equation between main cable force increment and internal force increment of the section also can be derived. According to the cross-sectional internal force equilibrium equation of the section and the relationship between stress and strain, the correlation equation between any section internal force increment and the surface strain increment of the pylon above lower cross beam are obtained. The increment of the main cable force can be calculated based on the parameters such as, geometric dimensions and material property of pylon column and main cable. The proposed method is used for the main cable force increment test in the static load test of Xixin bridge in Yongkang city, and a good practical effect is achieved. Combining with the example, the factors affecting the test accuracy of main cable force increment are analysed, i. e. , strain test accuracy, material property and cross sectional area of pylon, and angle between tangential direction of the main cable at pylon top and vertical direction. These parameters should be accurately measured or estimated in practice. The proposed method is simple and convenient, and the requirements placed on equipment and test conditions are low, which can provide a reference for main cable force increment test in the static load test in similar projects.