Rain-wind-induced cable vibrations in the Alamillo cable-stayed bridge (Sevilla, Spain). Assessment and remedial action

摘要

Rain combined with wind action provoking vibration has been observed in the longest stays of the Alamillo cablestayed bridge in Sevilla (Spain). The maximum displacements observed are in the order of magnitude of 0.5 m and have caused discomfort problems to the pedestrian circulation across the bridge. The paper shows the analytical and experimental studies carried out to analyse the possible solutions and also the steps developed to stop the vibration phenomenon. In 2004, a dynamic test in the cables was envisaged to measure the actual damping in the cables. It became clear that damping in the cables was very low and the solution required the installation of dampers. The damping devices had to be in accordance with the relevant aesthetic constraints of the structure. The installation of the damping devices took place during 2007. After the installation of the damping devices, a new dynamic test was carried out in February of 2008 to check if the level of damping introduced by the dampers was appropriate. During the tests performed in 2004, the natural frequencies of vibration were also obtained at the same time than damping. The comparison between the two sets of natural frequencies (1992 and 2004) allow to extract important conclusions about the correct performance and condition state of the bridge as well as the evolution of forces in the cables after 12 years of construction due to creep in the tower.