Effects of geometric imperfections on the performance of Sahand cooling tower

Abstract

During construction of one of the Sahand cooling towers due to slip forming performance some imperfections were raised mostly between elevation of +30 and +40 meter. It was evaluated that some points of the shell should be repaired. In constructing the cooling tower from elevation +40 to +60 meter these imperfections were removed and the cooling tower was constructed with no problem until the elevation +130 meter. In this paper reasons of generation of geometric imperfections in Sahand cooling tower are clearly shown and possible ways for preventing them are discussed. Applied repairing method for Sahand cooling tower is explained in detail. Geometrical imperfections of the constructed cooling tower are measured using photogrammetric techniques. The detailed three dimensional models for both perfect and imperfect cooling towers are made using finite element method. Different analyses for different loading of such structures are done and the results are compared. For the cooling tower with imperfections the wind load is applied in 12 directions around the circumference of it so that the effects of imperfections can be seen well. Critical buckling load factors are obtained for both models by linear and nonlinear analysis. The results of analysis of imperfect cooling tower shell are used for checking the design of it. Results show that the maximum values for circumferential and vertical stresses are appeared between level +30 to +40. The increase of circumferential stress is usually more than increase of vertical stresses. This high increase appears locally in some parts of cooling tower shell. The difference of displacements in cooling tower shell in two models is negligible. The critical buckling safety factor of the imperfect model is greater than the perfect one. There is not a large difference between the values of this factor for different wind load directions. © 2006 by School of Engineering and Technology, Asian Institute of Technology.