Abstract: The intermediate pylon of three-pylon cable-stayed spans lacks back-stays to limit its longitudinal displacement， which makes the structure more flexible.As a result.its deformation is so considerable that the whole structure's rigidity fails to the request of deform ation tolerance.According to the analy8i8 of a blue print of a three-pylon cable-stayed bridge across the Changjiang River with the finite element software MIDAS，making use of the available methods at present，a suitable method to improve the rigldity of this three-pylon cable-stayed spans is brought forth，which can be applied in other eonstradions like this.

Key words: three·pylon cable·stayed spans, rigidity, displacement, MIDAS

摘要： 三塔斜拉桥由于中间塔顶没有端锚索来限制它的水平变位，使得柔性结构斜拉桥的柔性进一步增大，随之而 来的是变形过大，整体刚度不能满足容许变形的要求.结合某长江大桥一三塔斜拉桥方案进行研究，借助已有改善 多塔斜拉桥刚度的方法，通过MIDAS计算分析对比，得出最适合此长江大桥刚度的改进方法，对其它地区三塔斜拉 桥的刚度改进方法有一定的借鉴作用.

关键词: 三塔斜拉桥, 刚度, 位移, MIDAS