多塔斜拉桥交叉索的纵向约束刚度

为明确交叉索对于提高多塔斜拉桥刚度的效果,建立带跨中交叉索多塔斜拉桥的力学模型.选取一个主跨作为隔离体,并将部分交叉索等效为竖向弹簧,研究交叉索的作用机理,推导交叉索对桥塔纵向约束刚度的解析公式.研究表明,当桥塔发生纵桥向位移时,梁段重量在交叉索中重新分配,导致交叉索的索力发生改变,从而产生对桥塔的约束作用.交叉索对桥塔的约束作用取决于交叉索的长度,水平投影长度以及交叉索的轴向刚度.建立三塔四跨有限元模型对解析公式进行验证,有限元结果与公式理论值符合良好,公式可有效估算交叉索的纵向约束刚度.数值分析表明,采用交叉索与增大桥塔或主梁刚度均能有效增大结构刚度,在桥塔及主梁刚度较低时,交叉索对增大结构刚度的效果尤其明显.

Longitudinal restraint stiffness of crossed cables in multi-tower cable-stayed bridge

In order to figure out the effect of crossed cables, mechanical model of multi-tower cable-stayed bridge with crossed cables was established. A single main span was selected as research object and part of the crossed cables were treated as vertical springs, mechanical mechanism of crossed cables was studied and an analytic formula for calculating the longitudinal restraint stiffness of the crossed cables was deduced. The study shows that, when the tower deformed in longitudinal direction, dead load of the deck was redistributed in the crossed cables and this led to the cable force change, leading to restraint effect for tower. The restraint stiffness of the crossed cables depends on the length of the cables, projection length in horizontal direction and its axial stiffness. A finite element model of cable-stayed bridge with three towers and four spans was established to verify the formula. The numerical method shows good agreement with the formula, which indicates the formula is effective in estimate the longitudinal restraint stiffness of the crossed cables. Numerical analysis shows that using crossed cables could increase the structural stiffness of multi-tower cable-stayed bridge as well as the tower and girder. The crossed cables play more important roles in increasing the stiffness of the structure if the tower and girder have low bending stiffness.