Stress resultants in hyperboloid cooling tower shells subjected to foundation settlement

Abstract

The effect of differential settlement of columns supporting a natural draught hyperboloid cooling tower on the stress resultants in the tower shell is analysed using discrete finite element modelling of the shell and the supporting base. The quadrilateral facet shell elements and 3-D beam elements are used to model the shell and the columns respectively. The stress resultants obtained due to an imposed settlement are compared with those reported earlier by other investigators. In the existing literature, the stress resultants are found using the Boussinesq equation to calculate the approximate edge loading (column forces) on the cooling tower shell due to differential settlement. It is shown in the present study that using the Boussinesq solution for the calculation of edge loading may lead to an over-estimation of the column forces and hence the stress resultants. The magnitude of stress resultants is also found to be dependent on the column flexibility. The paper also presents an investigation in which the local amplification of stress resultants in the vicinity of the shell-column junction of the cooling towers (stress concentration) due to dead load and foundation settlement is studied. It is shown that the stress concentration can be severe, i.e., up to seven times the average stress resultants for dead load, and upto five times the average stress resultants for the foundation settlement.