公铁两用斜拉桥斜拉索更换一体化技术研究

Research on Design-Construction-Monitoring Integrated Stay Cable Replacement Technology for Rail-cum-Road Cable-Stayed Bridge

针对公铁两用斜拉桥斜拉索更换设计-施工-监控一体化技术的空白,以国内首座公铁两用斜拉桥——芜湖长江大桥(主跨312 m双塔双索面矮塔斜拉桥,共128根斜拉索,采用1670 MPa直径7 mm镀锌平行钢丝,长41.624~123.042 m)的3根斜拉索(短索、中长索、长索)更换工程为背景,对涉及的设计、施工、监控技术进行研究。在斜拉索更换设计阶段,分别采用MIDAS Civil和ANSYS有限元软件建立全桥整体模型和被拆索的梁端钢锚箱局部模型,分析卸索和张索工况下的索力重分布、主梁线形、桥塔塔顶偏位、钢桁梁杆件应力、钢锚箱局部应力、轨道线形影响。计算结果表明:斜拉索更换过程中该桥各项参数(线形、索力、应力)均满足规范要求,换索过程可以保证结构及行车安全。斜拉索更换施工采用四级分级卸载和分级张拉的施工方法,确保了斜拉索更换时的结构状态变化缓慢可控。斜拉索更换施工过程中采取了全过程综合监测监控技术,对结构响应进行全过程监控。监控结果表明:斜拉索索力、主梁线形、杆件应力、桥塔塔顶偏位、铁路轨形指标的实测值与理论值吻合较好,且在规范要求的合理范围内。该桥斜拉索更换后结构响应及轨道形位均恢复至初始状态。

This paper presents the stay cable replacement practice of Wuhu Changjiang River Bridge and discusses the applicability of a design-construction-monitoring integrated stay cable replacement technology.The Wuhu Changjiang River Bridge is a two-pylon extradosed bridge with a main span of 312 m.The original 128 stay cables,measuring 41.624 to 123.042 m long,were composed of galvanized parallel steel wires of 7 mm diameter and with a nominal tensile strength of 1670 MPa.Three severely-deteriorated stay cables with different lengths were replaced,which were taken as study cases.In the replacement design stage,a general finite element analysis of the full bridge as well as a local finite element analysis of the steel anchor boxes in the deck were conducted in MIDAS Civil and ANSYS,respectively,to analyze the variation of multiple parameters during the demolition of the original stay cables and the tensioning of new stay cables,including the stay cable force redistribution,superstructure alignment,pylon head displacement,stresses in steel truss members,local stresses in steel anchor boxes,and rail track irregularity.As per the analyses,various parameters(alignment,stay cable force and stress)meet the code requirements,the structure is sound and vehicle travelling safety can be ensured during the stay cable replacement process.To make sure that the structural condition of the bridge could change slowly and under control during the stay cable replacement process,the original stay cables are demolished in four steps,while the new stay cables are also tensioned in four steps.A comprehensive monitoring and control technique was used for real-time monitoring and control of the structural responses during the stay cable replacement process.The results of the monitoring demonstrates that the measured and theoretical values of the key parameters,including the stay cable forces,superstructure alignment,stresses in steel truss members,pylon head displacement,rail track irregularity,agree well and are all within the allowable ranges.The structural responses of the bridge and track irregularity have restored to the initial state after stay cable replacement.