Lift or Across-Wind Response of Tapered Stacks

In the present study, the structure of the shedding forces from a slender tapered structure was studied in considerable detail in both smooth uniform flow and turbulent shear flow. From this study a simplified description of the forces in shear flow is developed and successfully employed to predict the response of an aeroelastic model. A significant finding is that the maximum response in the fundamental mode occurs when the shedding frequency at about one third of the stack height is equal to the natural frequency. The observations made during the study are employed to develop an equation that might be used to predict the behavior of full-scale structures. The significance of loads due to vortex shedding from tapered structures is examined. For typical concrete structures it is deduced that drag loads are likely to be dominant with regard to stresses over the lower 2/3 of the structures while vortex excitation of the second mode is likely to be the dominant consideration for the upper one third or thereabouts.