摘要
随着斜拉桥跨径的不断增大,斜拉索长度越来越长。斜拉索柔度大、质量小、结构阻尼低,极易在风荷载和主梁激励的作用下发生振动。风雨激振是在风和雨的共同作用下斜拉索发生的一种大幅、低频的振动,严重地危害到斜拉桥的安全性。由于问题的复杂性,其机理未有定论。在已有的风雨激振机理研究中,均采用准定常理论来确定拉索和水线上的气动力。本文通过风洞试验和理论分析手段,研究准定常理论在风雨激振研究中的适用性,全文共分为六章。
第一章为绪论。
第二章采用湖南大学风工程试验研究中心研发的三自由度强迫振动装置,进行了光拉索和粘贴水线拉索的刚性模型测压风洞试验。试验共包括六个工况:固定光拉索、竖向振动光拉索、粘贴水线的固定拉索、粘贴水线的竖向振动拉索、粘贴水线的扭转振动拉索、粘贴水线的竖向和扭转振动拉索。
第三章对风洞试验数据进行了详细的分析,得到了拉索和水线模型各测点的平均和脉动风压系数、功率谱密度函数、拉索和水线的三分力系数等。研究了Reynold数、竖向和扭转振动、水线位置角等对粘贴水线拉索的平均和脉动风压系数、三分力系数和旋涡脱落频率等的影响;比较了试验结果和准定常理论结果,结果表明:准定常理论得到的气动力反映了风雨激振气动力的主要特性。
第四章在风洞试验数据的基础上,对拉索的和水线的气动导数进行识别,得到了三个工况下拉索和水线的气动导数,并比较了通过气动导数得到的拉索脉动气动力和风洞试验测得的气动力。结果表明:通过气动导数得到的气动力的精度高于准定常理论得到的值。
第五章采用风洞试验的拉索和水线的三分力系数、建立了二维斜拉索风雨激振的两自由度刚性模型,对风雨激振的机理进行了详细的研究。
第六章为结论和展望。
With the increase of the span of cable-stayed bridges, stay cables accordingly become longer and longer. Stay cables are prone to vibrate under wind loads due to its large flexibility, small mass and low damping. Rain-wind induced vibrations of stay cables, which take place with large amplitude and low frequency under the combined action of the wind and rain, has severely affected the safety of cable-stayed bridges. As the complexities of this phenomenon, its mechanism is not fully understood until now. In the existing study of the mechanism of rain-wind induced vibrations, the aerodynamic forces acting on the cable and the rivulet are usually determined by the quasi-steady theory. This paper attempts to study the applicability of the quasi-steady theory by means of wind tunnel tests and theoretical analysis. There are six chapters in this paper.
Chapter 1 is the introduction.
In Chaper 2, A series of wind tunnel tests on a smooth cable model and a cable model with an artificial rivulet are carried out by using a 3-DOFs fored vibration system which is developed by the Wind Engineering Research Center of hunan university. There are six test cases, including fixed smooth cable, vertical vibration smooth cable, fixed cable with artificial rivulet, vertical vibration cable with artificial rivulet, rotational vibration cable with aritificial rivulet, and torsional-vertical coupling vibration cable with artificial rivulet. In Chaper 3, the mean and fluctuating wind pressures, power spectral densities of
fluctuating wind pressures, and three-components of aerodynamic forces of the cabe model and the artifical rivulet are obtained on the basis of the data from the wind tunnel tests. The effects of Reynold number, cable movement and rivulet position on the cable surface are studied in detail. Comparing the results of aerodynamic forces obtained from wind tunnel tests and quasi-steady theory, it is concluded that the quasi-steady aerodynamic forces reflect the main characteristics of the aerodynamic forces in rain-wind induced vibrations.
In Chapter 4, the aerodynamic derivatives of cale model and rivulet are obtained based on the data from the wind tunel test. The results show that the precision of fluctuating aerodynamic forces obtained from aerodynamic derivatives is higher than that of quasi-steady theory.
In Chapter 5, a 2-D imensional theoretical model of rain-wind induced vibrations with two degrees-of-freedom is established to investigate the mechanism of rain-wind induced vibations, in which the three-components of aerodynamic forces of the cabe and the rivulet are determined by quasi-steady theory.
Chapter 6 is the conclusions and advices on future works.
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