| Stay cable is one of the main components in cable-stayed bridges. It is easy to vibrate when subjected to environmental and traffic excitations because of its long span, large flexibility, small weight and low inherent damping ratio. The accurate analysis of the dynamic characteristics is one of essential tasks for the design of stay cables in cable-stayed bridges. The parameter vibration is a very important form in many complex cable vibration forms. The parameter vibration not only results in large displacement in the midspan of stay cable, but also enables cable force to change largely, which may lead to the aggravation of the fatigue failure of the cables.The effects of parameter vibration on the cable amplitude and force were emphatically studied in this paper, and other factors of measuring cable force by frequency method were also studied. Vibration measurement of part stay cables of Sifangtai Cable-stayed Bridge on Songhua River was carried out.The paper mainly consists of the following part:Numerical simulation of cable vibration was studied on the base of subsistent mathematical model of horizontal cable. Effects of many factors, including the initial tension, boundary conditions, excitation amplitudes, frequency ratio of excitation frequency and basic frequency of stay cable, damping ratio, cable length and so on, were studied on stay cable's maximum amplitude and force when the cable was excited along chordwise. Finite element model of stay cable was established. Some effects on cable force were analyzed, including the stay cable's sag, rake angle and occurring parameter vibration or not. The characteristics of time-dependent system ware returned to stay cables during the vibration process. The basic frequency time history and cable force time history were also extracted and analyzed during the vibration process.Factors of measuring cable force by frequency method were studied, and the applicable conditions of measuring cable force by frequency method were also analyzed. Tests and measurements of some stay cables'vibration were carried out on Sifangtai Cable-stayed Bridge on Songhua River. The vertical vibration displacement of the deck and the vibration frequency of stay cable in both inside and outside of the vibration surface were successfully measured. The effects of deck vibration on stay cables'tension and basic frequency were considered. The effects of sampling time and FFT length on frequency identification of stay cables were analyzed in detail. The method to induce the error of stay cables'basic frequency identification was discussed. |
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