Seminar - Mohammad Jonaidi - Effects of Differential Settlement on Storage Tank Shell

Wednesday, August 4, 1999, 3 - 4 pm
Civil Engineering Lecture Room 3

Abstract

In this thesis, attempts have been made to highlight the influence of the differential (uneven) settlement on the shell of closed and open-top steel storage tanks, with special attention given to understanding of the physical response of the practical cylinders, which have non-uniform shell thickness. Settlement is imposed as a vertical translation at the base, generally but not exclusively in the form of harmonic curves. Both theoretical and experimental investigations are carried out to fulfil this aim.

In theoretical approach, inextensional theory, membrane theory and semi-membrane theory have been applied for linear analysis of the shell. A simple expression has been developed for maximum meridional stress resultant at the bottom of the shell of closed-top tanks, verses maximum settlement. The Finite Element Analysis (FEA), as a most accurate solution, has been used to gain insight into the analysis of real cases, and to assess the effectiveness of the more limited solutions. Parametric results of FEA at three levels of taper (tmax/tmin = 1, 3 and 5) are presented in figures, providing immediately accessible solutions, and insight into understanding
The finite element analysis has also been carried out on the refined mesh models both in linear buckling and nonlinear approaches. Sensitivity of closed-top cylinders to circumferential restraints at the top has been figured out and then assessed in the numerical study. In a linear buckling parametric study the buckling of cylindrical panels, as a part of whole cylinder, have been investigated leading to developing an expression for critical stresses and critical settlements of cylinders under edge deformation. In limited geometries, the nonlinear and post-buckling behaviour of tanks under harmonic settlements have been studied with attention given to the effect of imperfection and internal pressures on the shell behaviour.

The experimental program has been conducted on seven precisely machined steel specimens of 600 mm diameter with uniform and stepped wall shells by using a test rig completely designed by researcher. Both open and closed top models have been tested under low imposed settlement in a linear approach and large settlement in the non-linear and post-buckling study. Particular attention has been given in the measurement of circumferential stresses developed in the girder of open top models and meridional stresses at the base of closed-top models. The buckling mode of shear form have been experienced in the uniform shells and at the top of stepped shell.