大跨铁路斜拉桥平行钢丝斜拉索锚杯调整量设计研究

Research on Adjustment Amount for Sockets of Parallel-Steel-Wire Stay Cables of Long-Span Cable-Stayed Railway Bridge

斜拉桥平行钢丝斜拉索锚杯长度一般根据锚杯内钢丝的锚固长度及其他构造尺寸确定,对于修正主梁线形偏差的调整量有限。针对大跨铁路斜拉桥中由施工、制造及桥上永久荷载偏差等导致主梁成桥线形偏差较大,而现行规范中的锚杯尺寸可能存在调整量不足的问题,以某千米级公铁两用斜拉桥为背景进行平行钢丝斜拉索锚杯调整量设计研究。采用悬索理论,分析道砟容重离散性引起的斜拉索索力偏差、斜拉索弹性模量偏差及斜拉索锚固点位置偏差对斜拉索无应力长度的影响,以确定合适的锚杯放张与张拉调整量。结果表明:对于铁路斜拉桥,现行规范规定的锚杯张拉调整量基本能够满足要求,放张调整量则可能存在不足;道砟容重离散性对斜拉索无应力长度影响相对最大,设计中应预留相应的锚杯放张调整量;对300 m以上的中、长索,还应考虑斜拉索索力偏差和斜拉索弹性模量偏差的影响,预留锚杯放张与张拉调整量;斜拉索弹性模量建议取2.0×10^(5) MPa,并考虑其在(1.9~2.1)×10^(5) MPa范围内进行设计。

The length of sockets of the parallel-steel-wire stay cables is usually dictated by the development length of steel wires in the sockets and the structural details of the anchorages,which contribute little to the adjustment of the geometry of the superstructure.For the long-span cable-stayed railway bridge,the geometrical bias of the superstructure after completion of the bridge is great due to the errors generated in the manufacturing and construction process as well as the beyond-design permanent loads,while the socket dimensions given in the current codes are undersized in terms of the required adjustment amount.A cable-stayed rail-cum-road bridge with a main span length exceeding 1000 meters is used as a case to study the adjustment amount of the sockets.The suspended-cable theory is used to analyze the influence of bias of cable forces triggered by the discreteness of the ballast density,elastic modulus and anchor points of stay cables on the unstressed lengths of the stay cables,based on which the proper de-tensioning and tensioning adjustment amount of the socket is determined.As per the analysis,the tensioning adjustment amount of the sockets specified in the current codes for the railway cable-stayed bridge can meet the requirements,while the de-tensioning adjustment amount is likely insufficient.Due to that the influence of discreteness of ballast density on the unstressed lengths of the stay cables is relatively the most significant,proper adjustment amount of socket de-tensioning should be reserved in the design.For the medium and long stay cables that are longer than 300 m,the influence of stay cable forces bias and elastic modulus of stay cables should be considered in reserving the de-tensioning and tensioning amounts of the sockets.The elastic modulus of 2.0×10^(5) MPa is suggested,and the design values should be within the range of 1.9×10^(5) MPa to 2.1×10^(5) MPa.