Analysis of Displacements and Stresses in Oil Storage Tanks Caused by Differential Settlement

Differential vertical settlement around the circumference of the foundations of large open-topped oil storage tanks can produce deformation of the tank including radial deflection of the tank shell. Excessive radial deflections may result in jamming of the floating roof. The results of an analysis by Malik et al. (1), based on the assumption that the behaviour of the shell is inextensional, are outlined. Two further analyses of the tank shell and the primary wind girder are presented. Both of these are simple, but use less restrictive assumptions than in reference (1). In the first analysis the shell is considered to act as a membrane. The second analysis makes use of a simplified version of the modified Donnell equation. The results of these analyses are compared with those of the analysis based on the inextensional behaviour of the shell. The limits of validity of the three different analyses are identified. It is proposed that the membrane solution is valid for all practical applications, and the results are presented in non-dimensional form in Fig. 6.