大跨度斜拉桥施工阶段抗风性能变化规律

大跨度斜拉桥是一种在风力作用下易发生变形和振动的柔性结构，其施工阶段结构抗风性能比成桥状态有所降低。采用数值模拟方法系统研究了大跨度斜拉桥单、双悬臂两大施工过程结构抗风性能的变化规律，包括结构动力特性及风致抖振响应。结果表明，随着单悬臂长度的增长，侧弯、扭转基频不断下降，侧弯基频降速较快，竖弯基频则在250m悬臂长度内呈现一个上升区段；随着双悬臂长度的增加，侧弯基频下降最快，竖弯和扭转基频下降速度呈现先变快后减慢的规律。当单悬臂长度在300m悬臂范围内，悬臂端部竖向抖振响应随悬臂长度基本呈线性增长；侧向抖振位移在200m悬臂长度范围内基本呈线性增长，超过200m之后，增速明显加快。当双悬臂长度在200m范围以内，抖振位移基本呈线性缓慢增长，当超过200m后，竖向抖振位移急剧增长，侧向位移增长速度亦加快，此时需充分考虑结构抖振响应对施工安全的影响。单悬臂端部抖振响应由主梁一阶模态起主要贡献，二阶模态亦有重要参与；双悬臂则以二阶振型，即对称振型起主要贡献。

Variation rule of wind-resistant behavior of long span cable-stayed bridges duringconstruction stages

Long span cable-stayed bridge is a kind of flexible structure which is sensitive to wind effects, especiallyduring construction stages. Variation rule of wind-resistant behaviors during two types of construction process,containing single-cantilever and double-cantilever construction stages, are studied via numerical methods. The resultsshow that the lateralandtorsionalfundamental frequency decrease with the increase of the single-cantilever length,while the vertical item presents a rising tendency until thecantilevelengthreaches250m. With the increase of thedouble-cantilever length, all the three fundamental frequencies decrease, among which the lateral item decrease mostdistinctly. Moreover, it is found that the vertical buffeting response increase linearly within the single-cantilever length of300m. The same variation rule appears for the lateral item until the single-cantilever length reaches 200m, out of whichthe lateral buffeting response increases distinctly. For the double-cantilever construction states, the limitation ofcantilever length for linear variation of buffeting response is about 200m. The buffeting responses of single-cantileverconstruction states are generally dominated by the first vibration mode of the girder and significantly influenced by thesecond mode. For the double- cantilever construction states, however, the symmetric mode dominates the buffetingresponse.