双主缆悬索桥体系中，塔顶位移及主缆的弹性伸缩均能引起主缆垂度的改变．文中假定连结上缆与下缆的吊杆不可伸缩，在塔顶位移及主缆弹性伸缩的共同作用下，上缆与下缆的竖向位移相等．基于此原理推导了双主缆悬索桥体系对桥塔顺桥向的约束刚度表达式及荷载在上缆与下缆之间的转移量与塔顶位移的关系，研究了单跨施加均布荷载时加载跨挠度的求解方法，给出了解析表达式，并建立有限元模型对公式进行了验证，模型值与理论值符合较好．

In the double- main cable suspension bridge system,the sags of the main cables change with the defor-mation of the pylon and the elastic extension of the main cables.Based on the assumption that the hangers of the top and bottom cables are inextensible,the vertical displacements of the top and bottom cables are equal when the de-formation of the pylon and the elastic extension of the main cables jointly play their roles.According to the above principle,this paper derives the expression of the longitudinal restraint stiffness of the bridge to the pylon as well as the relationship between the load transfer on the top and the bottom cables and the deformation of the pylon.Then,the solution method of the deflection of the load span under the uniform single- span load is investigated,and the corresponding analytical expression is obtained.Finally,all the formulas are verified by establishing a finite ele-ment model.It is found that the formulas accord well with the model.