大跨梁桁组合结构高铁斜拉桥主梁施工方案比选

Truss-Stiffened PC Box Girders for Long-Span High-Speed Railway Cable-Stayed Bridge

西十高铁汉江特大桥主桥为(67+70+73+420+73+70+67) m斜拉桥,主梁采用预应力混凝土箱梁和加劲钢桁架组成的梁桁组合结构,钢桁架下节点与预应力混凝土箱梁采用PBL键连接。边跨及塔区混凝土主梁采用支架现浇施工,为选择合理的中跨混凝土主梁施工方案,提出5 m节段悬浇施工、10 m节段悬浇施工、5 m节段预制悬拼施工3种方案,从建设条件、结构受力、行车动力性能、桥面线形、施工工期和投资等方面对3种方案进行对比。结果表明:5 m节段预制悬拼施工方案的工期最短,但投资最高,且受建设场地和运输条件的制约;节段悬浇施工技术成熟,技术风险及质量风险低,相比5 m节段,10 m节段悬浇施工方案虽然投资略高,但能够有效节省工期达5个月,且结构受力性能、行车安全性及舒适性、桥面线形均满足相关要求,在保证施工监控精度的前提下,成桥线形也在可控范围内,该桥最终选择10 m节段悬浇施工中跨混凝土主梁。

The main bridge of Hanjiang River Bridge carrying a section of the Xi′an-Shiyan High-speed Railway is a cable-stayed bridge with span arrangement of 67,70,73,420,73,70 and 67 m.The superstructure consists of prestressed concrete box girders stiffened with steel trusses,and the two are connected via PBL connectors.The concrete sections in the side spans and the pylon zones were cast in situ on scaffolds.Three construction options for the concrete box girders in the main span,including the 5 m-long-segment cantilever casting,10 m-long-segment cantilever casting and 5 m-long-precast-segment assembly,were compared from aspects of construction conditions,structural stress,vehicle loads,deck alignment,construction schedule and costs.It is shown that the 5 m-long-segment cantilever casting leads to the shortest construction schedule,but the highest costs,and the casting is restricted by the construction sites and transportation access.The segmental cantilever casting technique has been widely used in bridge engineering and proved effective in terms of low technical and quality risks.Compared with the 5 m-long-segment cantilever casting,the 10 m-long-segment cantilever casting results in higher costs,but allows a 5-month cut-down of construction time,and the related indicators,including mechanical property of the structure,train running safety and comfort,and deck alignment reach the required levels.Furthermore,considering the construction monitoring and control accuracy as well as the alignment of the bridge after completion,the 10 m-long-segment casting was finally selected for the concrete box girders in the main span.