HYPERBOLIC COOLING-TOWERS WITH BULGE IMPERFECTIONS

Owing to the large expanse of cooling towers, it is not possible to ma intain the exact shape of a tower during construction Alterations in s hape also occur due to secondary effects like shrinkage and cracking. These alterations cause the failure of some towers. This paper deals w ith the application of semiloof shell elements in the analysis of towe rs with bulge imperfections for both dead and wind loads. Four paramet ers, namely, (1) radial error amplitude, zeta m, (2) vertical location of bulge, Z(m), (3) vertical extent of bulge, h, and (4) angular exte nt of bulge, theta(m), have been identified as responsible in influenc ing 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 st udied Analysis suggests that the effect of bulge imperfections on stre ss resultants is localized, the development of hoop tension in the imp erfection zone is of primary concern, and stress changes induced are g reater if the imperfection is located closer to the base. Shorter wave length of an imperfection is more severe since curvature error is sign ificantly high for low wavelength. With increase in angular extent, th e change in hoop force is maximum for axisymmetric imperfection. Criti cal hoop stresses develop around the 70 degrees meridian, where high h oop tension and high meridional moments develop that can induce yieldi ng of hoop reinforcement and consequent failure.