Effect of Local Loads on the Stability of Shells Subjected to Uniform Pressure Distribution
Rules for design against buckling of shells according to current code cover only complete shell segments subjected to uniform or nearly uniform load distributions. The effect of initial imperfections is recognized but, local disturbances such as holes, local external forces or nonuniform stiffness distributions are not yet considered. Such disturbances are common in practical applications and may have a drastic influence on the carrying capacity of the shell.
The deflection of a shell caused by a small local load may be analyzed by use of linear shell theory. If it is assumed that its effect is equivalent to that of an initial imperfection, rules may be established for the analysis of the carrying capacity of the shell. This hypothesis was tested for cylindrical shells under axial compression through finite element analyses and tests on small scale plastic specimens and for spherical caps by computer analyses. It was found that the assumption is realistic and it yields, in its simplest form, slightly conservative results for cylinders but is nonconservative for spheres. Conversely, buckling tests on point loaded shells appear to give valuable information on the initial imperfection sensitivity and it may be possible to utilize such tests to develop more accurate guidelines on tolerances for manufacturing.
KeywordsFinite Element Analysis Cylindrical Shell Axial Compression Spherical Shell Point Load
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