ANALYSIS OF HYPERBOLIC COOLING TOWERS FOR GEOMETRIC IMPERFECTIONS

Abstract

Concrete natural draught cooling towers are one of the largest shell structures being built these days for power stations, chemical plants and other large industrial installations. The hyperbolic shell, with height and base diameter of 160 m and 120 m respectively these days, resistS the imposed wind load and gravity load primarily through development of membrane forces.. These reactions are in turn very sensitive to any changes in geometry of the structure. Given the huge extent of the structure, minor deviations from exact shape are unavoidable due to construction defects and secondary effects like shrinkage and cracking. The failure of the Fiddler's Ferry Tower in England has been attributed to an axisymmetric bulge in tower left during the construction. The very fact that these distortions can have such damaging effects call for analysis of the effect of geometric imperfections. Classical analytical solutions can be attempted with shells of regular geometry only. The problem of imperfections can be effectively analysed using Finite Element Method which is capable of handling local distortions in geometry. In this investigation, a Finite Element Analysis has been carried out in order to ascertain the influence of various parameters governing the geometry of a bulge imperfection, on the stress resultants in a tower.