超大跨径斜拉桥斜拉索局部振动对地震反应的影响

Effect of Cable Vibration on Seismic Response of Super-Long Span Cable-Stayed Bridge

在以往的斜拉桥地震反应分析中,大都采用单桁架(SECS)模型来模拟斜拉索,不能反映斜拉索的局部振动的影响.以世界第一跨度斜拉桥——苏通大桥为背景,采用多桁架(MECS)模型来分析斜拉索局部振动对超大跨度斜拉桥地震反应的影响,并探讨了斜拉索的合理单元划分方式.结果表明,斜拉索划分为10个单元已能够很好地反映斜拉索局部振动的影响.考虑斜拉索局部振动之后,会出现索梁耦合振型,减小一些振型的参与系数,基频与主梁的竖向振动相近的斜拉索在地震作用下大幅振动,而主梁和主塔的内力反应普遍减小,特别是主塔的地震轴力明显减小.

Single-element cable system （SECS） model is usually adopted in the seismic response analysis of cablestayed bridges, but the local vibration of cables cannot be simulated. A case study was made of the longest span cablestayed bridge in the world, the Sutong Bridge＇ to investigate the effect of cable vibration on seismic response. Its analytical model was established, in which, cables were modeled with multiple-element cable system （ MECS ）, and rational discretization manner was discussed. The results show that rational discretization manner divides each cable into 10 elements. Cable vibration change the dynamics characteristics of the whole bridge,especially, cable-deck coupled modes may appear by reducing the participation factors of some modes, the seismic forces of girder and tower decrease, especially the axial force of the tower. Furthermore, internal resonance makes the cables whose frequencies are close to vertical vibration frequency of the girder vibrate seriously.