Wind-Induced Lock-In Effects on Tall Circular Structures: Fid-Bau Portal

Wind-Induced Lock-In Effects on Tall Circular Structures

Arunachalam, Srinivasan

Vickery and Basu’s spectral method and Ruschewey’s method are widely used for prediction of vortex induced vibrations of circular structures. The aeroelastic interaction in Vickery’s method is accounted through a negative aerodynamic damping coefficient, while in Ruschewey’s method, it is taken care by an effective correlation length parameter. Both these parameters vary with response. The author had previously suggested a semi-empirical method, with a closed-form solution, for prediction of across-wind response under lock-in condition. The method was validated using experimental results from different wind tunnel and full-scale studies on chimneys. As a result of continued research, a modified mass damping parameter equal to $(\frac{2 m_{e}}{ρ D^{2}} \sqrt{η})$ \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left\{ {\frac{{2m_{e} }}{\rho{D^{2} }}\sqrt \eta } \right\}$$\end{document} was suggested as a useful parameter, which enables better prediction of across-wind response under lock-in condition for both RC and steel chimneys. An equation was earlier developed for the spectrum of modal overall lift force under non-lock-in region. Its modification under lock-in region was also suggested, using a parameter, “fact”. In this paper, the usefulness of the above equation is validated by considering wind tunnel test results reported by Kwok for a circular tower, located in a sub-urban terrain. A good agreement is obtained between the predicted modes generalized across-wind force spectral coefficients and corresponding test results by Kwok.