公铁两用钢桁架桥原位拓宽改建设计关键技术

以松浦大桥为背景,对公铁两用钢桁架桥原位拓宽改建的可行性及关键技术进行分析。松浦大桥原为双层桥面公铁两用钢桁架桥,上层布置2车道公路,下层布置单线铁路,为满足新的桥梁使用功能,将其上层公路拓宽为6车道,下层铁路改为非机动车道和人行道。由于道路规划限制,该桥主桥需基于原位进行拓宽且基础不能加固,故根据拓宽后结构增加的竖向荷载对原钢管桩基础进行验算,结果表明不加固基础,仅通过加固主桁架提高主桥上部结构的承载力是可行的。拓宽改建设计中采用构件贴板方案加固主桁架以提高上部结构的承载力;为改善结构受力,上层桥面系采用正交异性组合桥面板,下层桥面系采用整体式正交异性钢桥面;利用位于两侧桥台处的升降支架设置拉索以提高主桥的抗倾覆性能;综合考虑理论计算和施工控制,选择桥梁新、旧部分的上、下部结构连接方式;主、引桥均采用减隔震设计保证结构的抗震安全性。

Key Techniques for Design of In-Situ Widening and Reconstruction of Rail-cum-Road Steel Truss Bridge

Taking the Songpu Bridge as the engineering background, we analyzed the feasibility and key techniques of in-situ widening and reconstruction of the rail-cum-road steel truss bridge. The Songpu Bridge was originally a double-deck rail-cum-road steel truss bridge with a two-lane highway on the upper deck and a single-track railway on the lower deck. To meet the requirements of new traffic service function, the upper highway deck is widened to 6 lanes, and the lower railway deck is changed to non-motor vehicle lanes and side walks. Due to the limitation of road planning, the main bridge needs to be widened in-situ without reinforcing the foundation. Therefore, the mechanical properties of the original steel pipe pile foundation are checked and calculated according to the increased vertical loads after widening. The results show that it is feasible and practical to increase the bearing capacity of superstructure of the main bridge simply by enhancing the main truss itself without strengthening the foundation. In the design of widening and reconstruction, the main truss is reinforced with additional steel plates;in order to improve the structural stress distribution, an orthotropic composite deck is adopted for the upper deck, and a monolithic orthotropic steel deck is adopted for the lower deck;the lifting brackets located at the abutments on both sides of the bridge are used to set the cables to improve the anti-overturning performance of the main bridge;based on the theoretical calculation and construction control, reasonable connection mode between the widened and original structures for bridge superstructure and substructure are selected, respectively;the seismic isolation design is applied for both the main and approach bridges to ensure the seismic safety.