Hyperbolic Cooling Towers with Bulge Imperfections

Abstract

Owing to the large expanse of cooling towers, it is not possible to maintain the exact shape of a tower during construction. Alterations in shape also occur due to secondary effects like shrinkage and cracking. These alterations cause the failure of some towers. This paper deals with the application of semiloof shell elements in the analysis of towers with bulge imperfections for both dead and wind loads. Four parameters, namely, (1) radial error amplitude, ζ\im, (2) vertical location of bulge, \iZ\i\dm, (3) vertical extent of bulge, \ih, and (4) angular extent of bulge, Θ\i\dm, have been identified as responsible in influencing the behavior of imperfect towers. Their influence has been studied in detail and most critical geometry of the tower has been arrived at. The behavior of a tower with most critical geometry has also been studied. Analysis suggests that the effect of bulge imperfections on stress resultants is localized, the development of hoop tension in the imperfection zone is of primary concern, and stress changes induced are greater if the imperfection is located closer to the base. Shorter wavelength of an imperfection is more severe since curvature error is significantly high for low wavelength. With increase in angular extent, the change in hoop force is maximum for axisymmetric imperfection. Critical hoop stresses develop around the 70° meridian, where high hoop tension and high meridional moments develop that can induce yielding of hoop reinforcement and consequent failure.