大跨度钢桁拱桥三维激光扫描线形监控技术研究

3D Laser Scanning Technology Research for Erection Line-Shape Monitoring of Long-Span Steel Truss Arch Bridge

桥梁建设水平的长足发展导致桥梁施工体量和施工风险动态评估需求增大,大型桥梁架设过程中主桥线形监测至关重要,可保证主桥线形按照设计线形延伸。广州明珠湾大桥为六跨中承式连续钢桁架结构,架设过程中用全悬臂式施工法,悬臂长超过200 m的架设工况占比大,且大多数杆件在节点外采用高强螺栓拼接,杆件调整自由度大,在风、温度等多种自然因素影响下架设线形难以控制,而三维激光扫描技术能通过快速扫描获取海量结构物表面的坐标信息,实现结构中多个关键点位快速实时监测。以明珠湾大桥主桥架设过程为工程背景,采用三维激光扫描技术开展了钢桁架拱桥架设线形的监测研究。通过合理布置扫描仪监测位置,监测了主桥架设过程中主拱梁架设、主拱合龙、主梁合龙三个关键工况,重点在主梁悬臂端周围和塔吊周边开展多次结构扫描。监测过程中,运用后方交会法获取扫描仪架设位置坐标,推算监测目标的点云坐标信息,并采用点云处理软件Cyclone通过噪点消除、点云联合实现主桥点云整体模型拼接,进而结合点云数据处理技术提取多个线形监测指标进行分析,同时用全站仪获取相同点位坐标进行验证。结果表明:对于三维激光扫描和全站仪测量方法,主拱梁杆件悬臂端的桁间相对距离的平均差值为19 mm,在JTG/T F50—2011《公路桥涵施工技术规范》所容许的相邻点间相对点位测量误差内,说明基于三维激光扫描的线形监测方法可满足工程应用要求;塔吊节间垂直度指标总体在±3‰内,因此塔吊底部未达到极限弯矩,不会出现结构失效,但主拱梁大悬臂情况下塔吊上部结构出现了较大垂直度偏移,故仍需在主桥架设过程中加强监控;主拱和主梁的监测线形与设计线形基本吻合,横向、标高偏离指标的均值为2.9、16.6 mm,符合JTG/T F50—2011中钢拱桥纵轴与高差的偏位阈值,且主拱和主梁两侧悬臂杆在架设过程中不断趋近设计值,说明主桥架设线形控制良好,满足合龙需求。

The rapid development of bridge construction level leads to the increasing demand for bridge construction volume and construction risk dynamic assessment.Line-shape monitoring is crucial in the erection process of large steel truss arch bridge,which can ensure that bridge line-shapes accurately extend.Guangzhou Mingzhuwan Bridge is a six-span continuous steel truss structure with full cantilever construction method in the erection process.The erection working conditions account for a large proportion when the cantilever length is more than 200 m,and most of the rods are splice with high-strength bolts outside the joints in terms of the freedom of adjustment of the rods is large,so that the erection alignment is difficult to control under the influence of wind,temperature and other natural factors.The 3D laser scanning technology can obtain the coordinate information of massive structure surface through fast scanning,realizing the rapid real-time monitoring of multiple key points in the structure.The research has monitored the erection line-shapes of the main arch and girder of Mingzhuwan Bridge by using 3D laser scanning technology.Three key erection conditions of main arch girder erection,main arch closure and main girder closure were monitored through reasonable arrangement of scanner monitoring positions,and several structural scans were carried out mainly around the cantilever of main girder and around the tower crane.In the monitoring process,the rear intersection method was used to obtain the coordinates of scanner erection position and then calculated the coordinate information of the point cloud of the monitoring target.Moreover,the point cloud processing software Cyclone was used to realize the overall model splicing of the main bridge point cloud through noise elimination and point cloud association,and then multiple linear monitoring indicators were extracted for analysis by combining the point cloud data processing technology.At the same time,the same point coordinates were obtained by the total station for verification.The results show that the average difference of the relative distance between the cantilevers of the main arch and girder is 19 mm for the 3D laser scanning and total station measurement methods,which is within the relative point position measurement error between adjacent points allowed by Technical Specifications for Construction of Highway Bridge and Culverts(JTG/T F50—2011),indicating that the linear monitoring method based on 3D laser scanning can meet the engineering application requirements.The verticality index between the tower crane joints is generally within±3‰,thus the bottom of the tower crane does not reach the ultimate bending moment without structural failure.However,when the main arch or girder is large cantilever,the upper structure of the tower crane has a large vertical deviation,and it is still necessary to strengthen monitoring during the erection of the main bridge.The monitoring line-shapes of the main arch and girder are basically consistent with the theoretical line-shapes,and the mean values of transverse and elevation deviation indexes are 2.9 mm and 16.6 mm,which are in line with the deviation threshold of the longitudinal axis and height difference of steel arch bridges in JTG/T F50—2011.Moreover,the cantilever rods on both sides of the main arch and girder constantly approach the theoretical value during the erection process,indicating that the erection alignment of the main bridge well control and meeting closure needs.