EFFECT OF VARIOUS PARAMETERS ON AERODYNAMIC RESPONSE OF CHIMNEYS

Abstract

Chimneys are tall and slender structures and hence their design are governed mainly by horizontal forces. Wind forces are one of the major horizontal loads acting on the chimney. Wind forces acting on a chimney have two parts, one in the direction of wind or alongwind forces and the other in the perpendicular direction of wind or across-wind forces. The analytical method for calculating the alongwind response of a chimney has been suggested by Davenport and that for across-wind responses has been given by Vickery. The formulae for aerodynamic responses of a chimney are of semi-empirical type and they constAtute a number of parameters, which are not deterministic. This dissertation is a parametric study of aerodynamic behaviour of chimney. The parameters considered are, height of the chimney, large and small tapers of. chimney, structural damping, modulus of elasticity, terrain-roughness, choice of different energy spectra and wind velocity zones. The method of Davenport has been used to compute alongwind response and the across-wind responses have been computed using the method given by Vickery and Clark. Three heights of chimneys as 150 m, 200 m and 250 m • have been taken. For each height, two taper cases, viz the ratio of top-diameter to bottom-diameter as 0.4 and 0.6 has (vi) been taken to render cases of large taper and small taper respectively. Three values of modulus of elasticity, three values of structural damping and three types of terrains have been considered. For the computation of the along-wind dynamic response, the energy, spectra as suggested by Davenport, Harris and Kaimal have been taken. The across-wind response has been examined for two wind velocity zones, namely zone VI with basic wind speed of 55 m/sec and zone II with basic-wind speed of 39 m/sec.