VIV-galloping instability of rectangular cylinders: Review and new experiments

The interaction between galloping and Karman-vortex resonance for long rectangular cylinders is a crucial issue in flow-induced vibration, since this type of instability can cause catastrophic oscillations of structures or structural elements exposed to wind. Nevertheless, the models for galloping and vortex-induced vibrations fail to predict the onset of the excitation and its evolution with the flow speed. The main goal of this work is to clarify the most relevant features of the VIV-galloping instability for structures with rectangular cross section and to outline the parameters that control the phenomenon. First, this is pursued through an extensive literature review concerning two- and three-dimensional rectangular prisms with a side ratio in the range 1-2, which shows the complexity of the issue and the need for further investigations. Then, the results of new wind tunnel tests in smooth flow on a two-dimensional rectangular 3:2 cylinder were provided. This cross section was found very prone to instability and large-amplitude vibrations were observed also for high values of the Scruton number (product of non-dimensional mass times damping) and relatively low wind speeds. Also, for low Scruton numbers, the paper underscores the possibility to observe non-negligible excitation at low wind speed due to secondary vortex-resonance. Finally, the non-conservativeness of the values provided by Eurocode 1 for the galloping stability parameter and the Strouhal number is discussed. (C) 2014 Elsevier Ltd. All rights reserved.