Vertical vessel skirts generally have access openings. The evaluation for buckling of vertical vessel skirts shall consider the effect of the opening. On the other hand, evaluation methods of buckling in present design codes are established based on the theory for a cylindrical shell without any opening. There is no method to assess effects of openings on buckling strength. The purpose of this paper is to establish a new design method of vertical vessel skirts with access openings, by evaluating the effects of openings on buckling strength of cylindrical shells. The finite element analyses of buckling strength for cylindrical shells with and without openings were conducted by an eigenvalue analysis. A study was conducted on the effects of geometric parameters, such as skirt diameter, thickness, opening shape and application of reinforcements. The effects of openings on buckling strength were revealed by comparing the analysis results. Based on these results, the new design factor, Buckling Strength Reduction Factor (BSRF), was proposed for evaluating buckling strength. BSRF is the ratio of buckling strength of a cylindrical shell with an opening to that of a cylindrical shell without an opening. BSRF provides a practical simplified method to evaluate how an access opening affects skirt buckling strength.
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