中文摘要：

为了研究多跨悬索桥中塔纵桥向刚度,将主缆对桥塔的约束等效为弹簧,选定主缆及加劲梁的位移模式,通过虚功原理推导了主缆对中塔纵向弹簧约束刚度的表达式,建立有限元模型对公式进行验证,并与已有公式进行了对比。研究结果表明：弹簧刚度仅与主缆垂跨比及单位长度桥重有关,且与单位长度桥重呈线性关系,而受垂跨比影响较大;垂跨比减小时,主缆弹簧刚度迅速增大;推导得出的公式精度高,可以为初步设计阶段各参数的合理取值提供理论依据。

英文摘要：

In order to study longitudinal stiffness of middle pylon in the multi-span bridge,the main cable was treated as springs in considering its constraint to the tower.Displacement model was assumed and principle of virtual work was applied to deduce the analytic expression.And a finite element model was established and the comparison with the former one was made to verify its effectiveness.The research result indicates that the cable spring stiffness is related only to rise-span ratio and unit length weight of the bridge.There is a liner relation between cable spring stiffness and unit length weight.When rise-span ratio decreases,the main cable spring stiffness increases rapidly.Accordingly,the formula from it can be of high precision.The formula offer theoretical basis when proper parameters for multi-span suspension bridge in preliminary design stage are selected.