马鞍山公铁两用长江大桥主航道桥中塔下横梁抗扭设计

Torsional Resistance Design for Lower Crossbeam of Central Pylon of Main Navigation Channel Bridge of Maanshan Changjiang River Rail-cum-Road Bridge

马鞍山公铁两用长江大桥主航道桥为主跨2×1120 m的三塔钢桁梁斜拉桥,中塔采用钢-混组合结构,纵、横向均采用A形,为四肢空间桥塔,中塔横向两塔肢之间设置下横梁,2道下横梁之间通过3道系梁连接形成纵横梁结构,下横梁受扭问题较为突出。通过建立全桥总体有限元模型对下横梁受扭原因进行分析,结果表明:活载及纵向荷载作用下,桥塔发生弯曲,导致下横梁受到较大扭矩。结合纵横梁结构弯扭相互转化的受力特征,基于下横梁产生扭转原因及扭矩分配特点,建立下横梁扭矩计算模型计算下横梁所受扭矩,从满足结构受力和便于施工角度出发,分析了下横梁端部加高、边系梁加宽、箍筋分段局部加强3种下横梁抗扭设计方案,最终采用在下横梁截面外围布置2层闭合箍筋、下横梁箍筋分段局部加强的方案,该方案结构受力明确,安全合理,施工方便。

The main navigation channel bridge of Maanshan Changjiang River Rail-cum-Road Bridge is a steel truss girder cable-stayed bridge featuring its three pylons that create two equal main spans of 1120 m.The central pylon is a steel-concrete composite four-leg spatial pylon that looks like A-shaped structures from side and elevation views.Each two legs are connected by a lower crossbeam along the bridge width,and the two lower crossbeams are connected by three ties to form a latticed structure,however the lower crossbeams are under significant torsional forces.A finite element model of the full bridge was built up to analyze the causes of the torsion of the lower crossbeams.The results show that the pylon is prone to bend under the action of live loads and longitudinal loads,which bring the lower crossbeams under great torsional forces.The torsional forces imposed on the lower crossbeams were numerically simulated,considering the mutual transformation of bending and torsional forces in the latticed structure and the causes of the torsional rotation of the lower crossbeam as well as the characteristics of torsional moment distribution.Three modification schemes were proposed,including the scheme to increase the end depth of the lower crossbeam,the scheme to widen the edge ties and the scheme to locally strengthen the segmented stirrups,aiming to improve the load bearing capacity and ease the construction of the lower crossbeams.At last,the scheme to implement two layers of closed stirrups to enclose the cross-section of the lower crossbeam as well as segment and locally strengthen the stirrups was selected.After modification,the lower crossbeams are safer and easier for construction,revealing clear load transfer paths.