Modified Mass Damping Parameter for Better Prediction of Across Wind Response of Chimneys

Currently, Scruton number, Sc, is widely used as a single prime factor for prediction of across wind response of a circular chimney subjected to vortex shedding. It is however reported in the literature that there is a wide scatter in the variation of normalized response of different chimneys, when plotted against Scruton number. Vickery and Basu method is widely recommended for prediction of across wind response of RC chimneys, and Rusheweyh method is widely used for prediction of steel chimneys. However, there does not appear to be a single method which can equally predict the response of both steel and RC chimneys. The author has earlier developed a method for prediction of across wind response of circular chimneys, using a non-dimensional parameter “fact” and suggested a closed-form solution. In this paper, the usefulness and importance of a modified mass damping parameter (MDP) which has a slightly different form from the conventional Scruton number are focused and highlighted. It is shown that the suggested MDP has the potential of capturing the variation of response prediction for both steel and RC chimneys in a single curve. The spectral bandwidth, B, the turbulence intensity and “fact” parameter are also found to influence the response prediction besides Scruton number. The proposal of MDP is successfully applied to several full-scale and wind tunnel data in the literature, including author’s wind tunnel data.