Damping Identification of Bridges Under Nonstationary Ambient Vibration

This research focuses on identifying the damping ratio of bridges using nonstationary ambient vibration data. The damping ratios of bridges in service have generally been identified using operational modal analysis （OMA） based on a stationary white noise assumption for input signals. However, most bridges are generally subjected to nonstationary excitations while in service, and this violation of the basic assumption can lead to uncertainties in damping identification. To deal with nonstationarity, an amplitude-modulating function was calculated from measured responses to eliminate global trends caused by nonstationary input. A natural excitation technique （NExT）-eigensystem realization algorithm （ERA） was applied to estimate the damping ratio for a stationarized process. To improve the accuracy of OMA-based damping estimates, a comparative analysis was performed between an extracted stationary process and nonstationary data to assess the effect of eliminating nonstationarity. The mean value and standard deviation of the damping ratio for the first vertical mode decreased after signal stationarization.

空间缆斜拉—悬索协作桥合理成桥状态确定方法的研究

将斜拉—悬索协作体系拆分为斜拉子系统和悬索子系统,先分别确定两子系统的成桥状态再组合起来形成协作体系,这样易导致协作体系的成桥状态与子系统的受力状态不一致。基于无应力状态法的思路,保证组合前后受力状态一致的核心是控制各构件无应力状态量保持不变。分析了斜拉子系统和悬索子系统中缆索及斜拉索索单元无应力长度的计算方法,并通过温度补偿法抵消主梁和主塔的轴向压缩变形,实现对塔、梁单元无应力长度的修正;通过斜拉子系统成桥状态竖向位移在协作体系中设置预拱度,避免了主梁线形的变化对索力的影响;探讨了协作体系交叉区斜拉索与吊索索力的竖向分力的合理分配比例,为协作体系的拆分提供依据。形成了一套斜拉—悬索协作体系合理成桥状态的实现方法,并以某独塔空间缆斜拉—悬索协作桥为例对该方法进行了验证。结果表明,该方法解决了将子系统组合为协作体系时结构状态偏离目标状态的问题,实现了将复杂的协作体系拆分为悬索系统、斜拉系统进行计算的目标。