减小三塔悬索桥中塔顶主缆不平衡力的设计思路

Design Considerations for Alleviating Unbalanced Force of Main Cable atop Intermediate Tower of Three-Tower Suspension Bridge

针对大跨度三塔悬索桥在不利工况下中塔两侧主缆不平衡力较大的问题,以泰州长江大桥、马鞍山长江大桥、武汉鹦鹉洲长江大桥3座大跨度公路三塔悬索桥为例,分析该问题的解决思路。经分析,对于大跨度三塔悬索桥,中塔采用钢塔或钢-混凝土叠合塔;加劲梁在中塔处设置纵向约束;鞍槽内主缆抗滑安全系数K在1.5～2之间取值（实际K≥1.2已足够安全）的设计思路对减小该类桥梁中塔顶主缆不平衡力有利。另外,建议对极端加载工况（一个主跨满布活载、另一个主跨空载）的活载进行额外的合理折减;不连续主缆的设计也是可以考虑的思路。

In view of the problem that the unbalanced force of the main cable on both sides of the intermediate tower of long span three-tower suspension bridge under the unfavorable load case is great, three long span highway three-tower suspension bridges of Taizhou Changjiang River Bridge, Maanshan Changjiang River Bridge and Wuhan Yingwuzhou Changjiang River Bridge are cited as the examples and the considerations for solving the problem are analyzed. Based on the a- nalysis, it is believed that for a long span three-tower suspension bridge, the design considera- tions, including the utilization of the steel or steel and concrete composite intermediate tower, ar- rangement of the longitudinal restraints for the stiffening girder at the intermediate tower and se- lection of the K value of the slip resistance safety coefficient in the range of 1.5～2 （actually, K≥ 1.2 is sufficiently safe）, for the main cable in the saddle trough are helpful to alleviate the unbal- anced force of the main cable atop the intermediate tower of such type of the bridge. Besides, for the live load under the extreme load case （a main span fully with live load while a main span with empty load）, it is proposed that the live load should be additionally reasonably reduced and the de- sign of the discontinuous main cable should also be a way that can be considered.