九江长江公路大桥北塔下横梁施工方案研究

Construction Scheme Study of Lower Cross Beam of North Pylon of Jiujiang Changjiang River Highway Bridge

九江长江公路大桥主桥采用(70+75+84)m+818m+(233.5+124.5)m双塔不对称混合梁斜拉桥,H形桥塔塔肢间设上、中、下3道横梁。为确定该桥北塔下横梁施工方案,对同步施工方案、异步施工方案、异步施工+主动横撑方案进行分析。结果表明:异步施工+主动横撑方案结构受力合理、施工工期短、施工风险小,确定为下横梁最终施工方案。经优化,主动横撑采用2根1 200mm×12mm的螺旋焊管制作,每根施加2 000kN水平推力,在下横梁第一层混凝土强度达到90%之后,施加第一批横向预应力前撤掉水平推力;采取增加塔柱混凝土凿毛厚度、加强局部振捣的方法,保证新老混凝土结合面混凝土的施工质量。

The main bridge of Jiujiang Changjiang River Highway Bridge is a two-pylon asym- metrical hybrid girder cable-stayed bridge with span arrangement of （70＋75＋84） m＋818 m＋ （233.5＋124.5） m. The H-shaped pylon of the bridge is equipped with three cross beams： the upper, the intermediate and the lower cross beams. To determine the construction scheme for the lower cross beam of the north pylon, the schemes of synchronous construction, asynchronous construction and asynchronous construction plus active cross brace are analysed. The results of the analysis indicate that the scheme of asynchronous construction plus active cross brace prevails over the other two schemes, it can cut down construction time and reduce the construction risk, and the addition of active cross brace improves the stress condition at the base of the bridge py- lon, which is finally determined as the construction scheme for the lower cross beam. After opti- mization, the active cross brace is made from 2 spiral welded pipes of 1 200 mm×12 mm in diameter, and each pipe is applied with a horizontal push of 2 000 kN. When the intensity of the first layer concrete of the Lower cross beam reached 90%, the horizontal push was removed, then, the tensioning of the prestress of the first batch of cross beams began. To guarantee the construc- tion quality of the concrete at the old and new concrete interface, the method of increasing the chiseling thickness and intensing local vibrating of the pylon leg concrete was adopted.