基于激光扫描实测索形的斜拉索索力测量方法

Measurement Method of Stay Cable Force Based on Measured Cable Shape Using Laser Scanning

为了解决现有的斜拉桥索力测量方法在精度、可靠性、效率等方面仍存在的不足,首次提出了一种由实测索形直接估计索力的新方法,简称索形法。采用在斜拉索上任意截取的拉索节段构建了悬链线力学模型,基于悬链线公式,首次推导了由实测索形点集精确估计拉索张力的计算公式。地面激光扫描技术被研究用于快速捕获斜拉索索形,开发了基于扫描点云自动化精确提取拉索中心线的算法。以在建的水土嘉陵江大桥为试验对象,详细分析了三维扫描测量误差、拉索截面弯曲刚度及边界条件和拉索局部弯曲变形、拉索振动等索形偏差因素及其对索力计算精度的影响。研究结果表明:已知拉索直径条件下,三维扫描实测索形误差为0.000 4~0.001 5 m之间,测量误差引起的索力计算误差在0.2%以内;拉索弯曲刚度与锚固边界条件引起的索形与标准悬链线形的偏差较小,对索力计算精度的影响可以忽略不计;当拉索自振振幅小于R/4时,三维扫描仍能精确测量拉索的索形;在多种索形偏差的叠加下,所提出的索力计算方法能够实现数值计算的最优估计。对比索形法和被精确标定的千斤顶的测试结果表明,索形法的索力测量值与千斤顶测量值吻合,最大偏差为0.9%,证明了该方法具有较高的索力测量精度;与频率法对比结果表明,所提出方法的数据采集效率提高了8倍,并且具有自动化程度高、测量风险低、测量结果可靠性强等优点。

To solve the problems of accuracy, reliability, and efficiency of existing cable force measurement methods for cable-stayed bridges, a new method for estimating the cable force directly from the measured cable shape is proposed for the first time in this study. The catenary mechanical model was constructed for an arbitrary section of the stay cable. Based on the catenary formula, the calculation formula for accurately estimating the tension of the stay cable from the measured cable shape point set is derived for the first time. Terrestrial laser scanning technology is used to capture the shape of the stay cable quickly, and an algorithm for automatic and accurate cable centerline extraction based on a scanning point cloud is developed. Taking the Shuitu Jialing River Bridge under construction as the experimental object, the influence of the 3 D scanning measurement error, bending stiffness, boundary conditions of the cable section, and local bending deformation of the cable and cable vibration on the calculation accuracy of the cable force are analyzed in detail. The results show that under the condition of known cable diameter, the error of cable shape measured by 3 D scanning is between 0.000 4-0.001 5 m, and the calculation error of cable force caused by measurement error is less than 0.2%;the deviation between cable shape and standard catenary caused by cable bending stiffness and anchoring boundary condition is small, and the influence on the calculation accuracy of cable force can be ignored;when the natural vibration amplitude of the cable is less than R/4, the shape of the cable can still be accurately measured by 3 D scanning;under the superposition of various cable shape deviations, the proposed cable force calculation method can achieve the optimal estimation of numerical calculation. The test results of the cable shape method and the accurately calibrated jack show that the cable force measured by the cable shape method is consistent with that measured by the jack, and the maximum deviation is 0.9%, which proves that the method has higher cable force measurement accuracy. Compared with the frequency method, the results show that the data acquisition efficiency of the proposed method are increased by eight times, and it has the advantages of a high degree of automation, low measurement risk, and strong reliability of measurement results.