Regen‐Wind‐induzierte Schwingungen – ein State‐of‐the‐Art Report

Rain‐wind induced vibrations can occur, when rain and wind simultaneously act, for instance, on the cables of cable‐stayed bridges, on inclined steel hangers of arch bridges or on the backstays of guyed masts. As a result of wind and gravity, the rainwater forms small rivulets, which flow down on the surface of these structural members. The rivulets disturb the wind flow around the dry cross section and cause a modified unsymmetrical distribution of the surrounding wind pressure, which leads to periodic exciting forces. Due to the movement of the cable and the wind forces, the position of the rivulets varies on the cable surface. This constellation can lead to aeroelastic excitation with large amplitudes. Rain‐wind induced vibrations can reduce the life cycle of a structure seriously, because the initialising wind velocity of rain‐wind induced vibrations is significantly lower than the design wind velocity and thus has a high probability of occurrence. In this paper, the further researches and investigations up to now dealing with rain‐wind induced vibrations are summed and commented.     

Regen‐Wind‐induzierte Schwingungen – Ein Berechnungsmodell auf der Grundlage der neuesten Erkenntnisse

Rain‐wind induced vibrations – a calculation model based on recent investigations. Rain‐wind induced vibrations of slender structural members with circular cross sections, as of bridge‐cables or hangers of tied arch bridges may occur when these members are exposed to both wind and rain. This vibration phenomenon is known to bridge‐engineers after the spectacular closing of the Erasmus Bridge shortly after inauguration and the damages at hangers of the Dömitz Bridge across the river Elbe. For the onset of rain‐wind induced vibration various parameters as the intensity of rain, the wind velocity and the wind direction in relation to the slope of the member play an important role. Vibrations once die away, when the intensity of rain or the wind velocity change significantly or the wind direction varies. Rain‐wind induced vibrations are self‐induced vibrations where the inducement mechanism from the variation of the position of the rain rivulets interacts with the movements of the cables or hangers. This type of vibration is not novel, however the mechanism has so far not yet been sufficiently investigated to produce a calculation model that allows predicting the magnitude of the vibration amplitudes.     

Praktisches Verfahren zur Bemessung von Brückenseilen und ‐hängern zur Vermeidung Regen‐Wind‐induzierter Schwingungen

A semi‐empirical method for the design of bridge cables and bridge hangers in order to avoid rain‐wind induced vibrations. Rain‐wind induced vibrations have been widely studied during the last decades. Today it is desirable to use the experience gathered in this filed in order to develop a practical design procedure offering both security and economy. After a restricted review of some analytical models, this paper points out the need for a semi‐empirical method if the complexity of this design procedure has to be kept at its minimum. Based on measured data collected during field tests and wind tunnel experiments, a new proposal is suggested.