考虑套管影响的钢绞线斜拉索索力测试方法

A Method for Testing Steel Strand Stay Cable Force Considering Influence of Casing

平行钢绞线斜拉索一般采用单根牵引、单根张拉的方法施工,具有现场安装及张拉工艺简单、施工便捷等优点,同时后期维护时易于更换,使其在国内外斜拉桥建设中得到广泛的应用。在斜拉索张拉过程中,HDPE外套管的影响使得采用频率法测定钢绞线斜拉索索力时产生较大误差。为研究HDPE外套管对钢绞线斜拉索索力测试产生的影响,以息县淮河大桥为背景工程,综合考虑外套管环向约束作用和自重挤压接触作用两种因素,分析外套管与内部钢绞线接触后对钢绞线斜拉索自振频率的影响,并对拉索-频率常用计算公式进行修正。结果表明:斜拉索张拉过程中HDPE外套管的自重主要由外围钢绞线承担;斜拉索自振频率大小和外套管与内部钢绞线接触的数量有关,与外套管发生接触的钢绞线自振频率小于未与外套管发生接触的钢绞线同阶次自振频率,高阶模态中塔端、梁端位置会出现干扰振型;由依托工程现场实测数据可知,考虑外套管影响修正后的索力测试结果与实际张拉力基本一致,综合考虑外套管环向约束作用和自重挤压作用修正后的拉索-频率计算公式可用于实际工程。

Parallel steel strand stay cables are usually constructed by single traction and single tension method, which has the advantages of simple installation and tension process on site and convenient construction. At the same time, it is easy to replace in later maintenance, which makes it widely used in cable-stayed bridge construction in China and abroad. In the process of cable tension, due to the influence of HDPE casing, there is a large error when using frequency method to measure the cable force of steel strand stay cable. In order to study the influence of HDPE outer casing on the test of steel strand stay cable force, taking the Huaihe River Bridge in Xixian County as the background project, considering the factors of outer casing hoop constraint and dead weight extrusion contact, the influence of the contact between outer casing and inner steel strand on the natural frequency of stay cable is analyzed, and the common calculation formula of the cable-frequency is modified. The result shows that(1) in the process of cable tension, the dead weight of HDPE outer casing is mainly borne by the outer steel strand;(2) the natural frequency of stay cable is related to the number of contact between the outer casing and the inner steel strand, the natural vibration frequency of the steel strand in contact with the outer casing is less than that of the steel strand not in contact with the outer casing at the same order, and the interference mode will appear at the pylon end and the beam end in the high-order mode;(3) it can be seen from the measured data of the project site that the tested modified cable force considering the influence of the outer casing are basically consistent with the actual tensile force, and the modified cable-frequency calculation formula considering the circumferential constraint of the outer casing and the dead weight extrusion can be used for practical project.