Dynamic behaviour under Wind loading of a 90m Steel Chimney This report presents results from an investigation of the structural behaviour of a 90 m high steel chimney equipped with a mechanical damper at the top. Due to a mistake in installing the chimney the damper was not active in the first period of service life, causing large oscillations of the structure and fatigue cracks to occur within a few months of service. Because of this an extensive investigation was started to rectify the action of the damper, repair the steel structure and to monitor the behaviour of the structure adopting a fail-safe