The mechanism of rain-wind-induced vibration

The phenomenon of rain-wind-induced vibrations has become more and more important not only for cable stayed bridges but also for vertical hangers of arc bridges and cables of suspended large roofs. Several investigations have been undertaken to clearify the exciting mechanism starting with the pioneering work of Hikami/Shiraishi 1988 up to the most plausible explanation given by Verwiebe 1998, who also proposed a rough estimation for the calculation of the expected vibration amplitude. There is a three mass aero-hydro-elastic interaction between the vibrating cable, the wind and the oscillating water rivulet which induces the exciting forces. The different rivulet configurations induce different vibration modes — in-wind and cross-wind direction. Model tests as well as full-scale observations (Luesse et.al. 1996) show the range of significant excitations depending on the inclination of the cables, the natural frequency of the cable, the wind speed, the wind direction and the structural damping. A first step for the development of a mathematical model for the practical application of the prediction of the vibration amplitude is presented.