Buckling strength of imperfect ring-stiffened cylinders under combined loads

Khaw, Teik Seng (1980) Buckling strength of imperfect ring-stiffened cylinders under combined loads. PhD thesis, University of Glasgow.

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Abstract

Two computer programs, one for interframe collapse and the other for overall collapse as influenced by initial imperfections, have been developed and the results compared with experiments and with present design codes. A treatment is presented for the buckling strength analysis of ring stiffened cylinders under external hydrostatic pressure and axial compression. The energy method by Ritz approach is used because of its adaptability to the solution of complicated buckling forms. Equations accounting for non-uniform and uniform lateral pre-buckling displacements are presented in this thesis. The effect of uniform and non-uniform lateral pre-buckling displacements on collapse pressure under uniform external pressure is shown by means of numerical examples. Such effect does not yet appear to have been carried out. Comparison with classical Von Mises equation for elastic buckling under uniform external pressure is good for the case of uniform lateral pre-buckling displacement. Factors such as initial shape imperfections due to fabrication, welding and cold-bending residual stresses of the shell are considered. The technique used to model such imperfections is solely the author's original contribution. An approximate method using the secant modulus is introduced to account for inelastic behaviour. These factors are considered to be the most important adverse features which distinguish offshore structural response from that of aerospace structures. The effect of strain reversal is assumed to be small and negligible. Ideal elastic perfectly plastic behaviour (with no strain hardening) is assumed for the material. Quantitative imperfection studies defining the sensitivity of inter-frame shell buckling to the form and amplitude of initial distortion and residual stresses have been carried out. Such studies do not yet appear to have been carried out. The effects of initial geometrical shape imperfections are shown to be most serious with axial compressive load. This is followed by external pressure and the less sensitive radial (lateral) pressure loading. A study of the effects of welding residual stresses on interframe collapse pressure under uniform external pressure confirms that the compressive welding residual stresses of the shell is detrimental to buckling strength of cylindrical shells. The cold-bending residual stresses in the shell have negligible effect on the collapse pressures of the shell. Comparisons are made with the BS5500 design code and the DnV Rules for interframe collapse. For overall collapse comparison with BS5500 design code is included. Results obtained by the present theory are also compared with results obtained by finite difference dynamic relaxation and finite element methods. Comparisons with experimental data for both interframe and overall collapse behaviour under uniform external pressure demonstrate good agreement with the theory.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D Faulkner
Keywords: Ocean engineering, Mechanical engineering, Petroleum engineering
Date of Award: 1980
Depositing User: Enlighten Team
Unique ID: glathesis:1980-74169
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Sep 2019 15:33
Last Modified: 23 Sep 2019 15:33
URI: http://theses.gla.ac.uk/id/eprint/74169

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