Rain–wind induced vibrations – phenomenology, mechanical modelling and numerical analysis

The simultaneous appearance of rain and wind at cables of cable stayed bridges and hangars of arch bridges may induce varying oscillations with large amplitudes. These phenomena are identified as rain–wind induced vibrations. The paper presents a possible fluid-mechanical interpretation of rain–wind induced vibrations. Based on this interpretation a mechanical model is deduced, in order to enable numerical investigations. The complex system of nonlinear differential equations is analysed concerning the stability of solutions. Rain–wind induced vibrations exist only within a certain range of wind velocity. The lower limit of the critical velocity range is determined for various cable inclinations and angles of incidence. Furthermore, a fluid mechanical interpretation is given for the existence of the upper limit of critical velocity. The approximation of the upper limit velocities and the determination of the critical cable diameters can be derived from established fluid-mechanical correlations. The numerical investigations show that rain–wind induced oscillations occur on vertical cables, too. For the Faro–Falster Bridge, the numerical vibration analysis is carried out for the cables parallel and perpendicular to the wind direction. The analysis of the vibration frequencies is demonstrated for the Dömitz Bridge.