| The first part of the thesis, consisting of Chapters 3--5, presents the results of theoretical studies into the characteristics of geometric imperfections measured in three large steel silos at Port Kembla, Australia, and their effect on buckling strength. In order to accurately represent these imperfections measured at non-uniformly spaced sampling points, a new iterative Fourier decomposition method was proposed. The traditional Fourier decomposition method cannot produce accurate Fourier representations, and the reasons for this difficulty are clarified in the thesis. This new iterative method was then employed in deducing accurate Fourier series representing the measured imperfections. It is explained in the thesis that these real imperfections, due to their non-zero values at the boundaries, can only be accurately represented using half-wave cosine series in the meridional direction, an important phenomenon overlooked by all previous researchers.;While detailed measurements of imperfections are available for the three large silos, the residual stresses in these shells due to welding are unknown. As residual stresses may have a significant effect on the buckling strength, an experimental study aimed at an indirect evaluation of this effect is presented in Chapters 6--8. In this experimental study, an innovative two-stage model fabrication technique was proposed and implemented with a sophisticated experimental set up for the fabrication of small models simulating large cylindrical shells with many welds.;Finally, a parametric study is presented in Chapter 9, in which the buckling behavior and strength of the three real silo shells under the combined action of axial compression and internal pressure were explored. Nonlinear finite element analyses revealed that the strengths of Shell A are considerably lower than those of Shells B and C, as the dominant imperfection components are significantly axisymmetric in Shell A, but are highly non-symmetric in Shells B and C. Comparisons between the finite element results and the predictions of Eurocode 3 indicate that the code overestimates the failure strengths of Shell A considerably. Modifications to the existing design rule are thus presented to achieve safe predictions. (Abstract shortened by UMI.)... |
