卢沟桥形变监测分析

The analysis for the deformation monitoring of Lugou bridge

针对我国古代石拱桥因长期自然环境作用及人为破坏等因素出现较多结构病害,以及年代久远、缺乏设计资料等原因,急需有效的技术方法获取关键结构参数并进行结构状态评估的问题,该文提出一种基于三维点云的古石拱桥关键结构参数识别方法。以北京卢沟桥为研究对象,利用三维激光扫描的空间坐标数据建立了拱轴线的自动迭代拟合算法,在此基础上,开展了拱圈矢高、跨径和矢跨比等关键结构参数的识别与分析。结果表明,卢沟桥的拱轴线线形为圆弧线,各拱圈矢跨比均在0.37以上,均属陡拱;卢沟桥各拱圈的上、下游之间已产生相对变形,以拱5最为显著;卢沟桥顺桥向各拱圈的结构对称性已有显著改变,拱11和拱1之间的净矢高与净跨径偏差值分别为252.4 mm和380.7 mm。分析结果可为北京卢沟桥的后续保护提供依据,该文方法也可为类似石拱桥的维修保护提供技术支持。

Aiming at the problem that ancient stone arch bridges have many structural diseases due to long-term environmental effects and man-made damage, and because of long-term service time and lack of design materials, structural condition evaluation calls for effective technology to obtain the critical structural parameters of the ancient stone arch bridges. An identification method of critical structural parameters was proposed based on 3 D point cloud for ancient stone arch bridges. The Lugou bridge in Beijing was taken as the case-study bridge in this paper. The automatic iterative fitting algorithm of the arch axis was developed based on the bridge spatial data obtained by using 3 D laser scanning. The critical structural parameters, including arch rise, arch span and rise-span ratio were identified and analyzed. The results supported that the profile of the arch axis of the Lugou bridge belonged to circular curve. All 11 arches in the Lugou bridge could be classified as steep arches because the rise-span ratio of all arches was more than0.37.Obvious relative deformation could be observed between the upstream side and downstream side of each arch ring and the maximum relative deformation could be found in arch 5.In the longitudinal direction,the structural symmetry between the arches had changed.The differences of clear rise and clear span of arches 11 and 1 were 252.4 mm and 380.7 mm,respectively.The results could provide reference for the follow-up protection.The proposed method could provide technical support for maintenance and protection of the similar ancient stone arch bridges.