The main bridge of Maanshan Changjiang River Highway Bridge over the left branch is a three-tower suspension bridge with main span arrangement 2 × 1 080 m. To resolve the problem of considerable cable force differences of the main cables at either side of the intermediate tower of the bridge due to the action of unbalanced load, the rational structural system should be appropriately selected. Four types of the structural systems of the tower-to-girder rigid fixity, bearing restraint, semi-floating and complete floating are compared and analyzed and the finite element software BNLAS is used to analyze the mechanical behavior of the structural systems. The results of calculation indicate that the slip resistance safety coefficient of the tower-togirder rigid fixity system is the highest and the structural rigidity is the greatest. The stress in the part of steel structure of the intermediate tower is within the allowable range, the wind resistance and seismic resistance performance are superior to those of the floating systems and the arrangement of bearings is not necessitated. The cable force differences of the four structural systems are very little. The stress in the stiffening girder of the tower-to-girder rigid fixity system is great, but it can be controlled by adjusting the depth of the girder. Through the comprehensive comparison and selection, the tower-to-girder rigid fixity structural system is eventually chosen for the bridge.%马鞍山长江公路大桥左汊主桥为主跨2×1 080 m的三塔悬索桥,为解决该桥在不平衡活载作用下引起中塔两侧主缆缆力差值较大的问题,需要选择合理的结构体系,对塔梁固结、支座约束、半飘浮与全飘浮4种结构体系进行对比分析.采用有限元软件BNLAS分析4种结构体系的力学特性,计算结果表明:塔梁固结结构体系抗滑安全系数最高、结构刚度最大、中塔钢结构段应力在容许范围内、抗风与抗震性能优于飘浮体系、不需要设置支座;4种结构体系在缆索受力方面差异很小;塔梁固结体系加劲梁受力较大但可以通过调整梁高来控制应力.经综合比选,该三塔悬索桥最终采用塔梁固结的结构体系.
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