Buckling Design of Ring-Stiffened Cylinders

ABSTRACT The paper reports on a study carried out by J.P. Kenny & Partners on behalf of the U.K. Department of Energy to update the Guidance Notes relating to the Buckling of Offshore Steel Structures. The Guidance Notes will be incorporated in the revised edition of the Department of Energy document "Offshore Installation : Guidance on Design and Construction". Ring-stiffened cylinders formed one of five categories of structural elements investigated by the authors in the course of the study. The paper presents comprehensive collections of test results gathered from all available sources worldwide relevant to the buckling of unstiffened and ring-stiffened cylinders under axial, pressure and combined loadings. The collated results are compared with the corresponding predictions from various Code Recommendations. All forms of collapse, such as inter-ring shell buckling, general instability and ring-stiffener failure are considered. Conclusions are drawn as to the validity and implied safety of these Design Recommendations and gaps in the available experimental and design information are identified. 1. INTRODUCTION The department of Energy of the United Kingdom issues technical guidance on a wide range of subjects, primarily to help ensure the safety of engineering systems in a offshore environment. The guidance is supplied in the form of conclusions derived from knowledge of the state-of-the-art pertaining at the time of issue. Due to the information gained by advances in the application of technology to new or expanding fields, and/or the results of theoretical or experimental research programmes in a given area, the Guidance Notes need up-dating or revision from time to time. The work presented in this paper stems from a study sponsored by the Department of Energy in order to up-date its Guidance Notes relating to the Buckling of Offshore Steel Structures [7]. These notes will be incorporated in the revised edition of the Department of Energy document "Offshore Installation : Guidance and Construction". Ring-stiffened cylinders formed one of the five categories of structural elements investigated by the authors which formed the basis of this study. Together, these comprise the main structural elements utilized in the construction of steel offshore installations and are as follows:Unstiffened Chord and Bracing ElementsRing-stiffened CylindersStringer and Orthogonally-stiffened CylindersUnstiffened and Stiffened Flat PanelsEnd Closures and Transition Shells Part of the study was to collate all of the available experimental data relating to the buckling behavior of the structural elements in each of these five groups. Relevant theoretical and numerical results were also considered. The collated experimental data was compared with the corresponding values as calculated by the various Code Recommendations currently in use for offshore design. These include DnV, ECCS, ASME, API, BS5500 and DASt Recommendations, References [1-6]. In this way, the data could be used as a yardstick to gauge the validity of any given recommendations and could also indicate where code revisions were necessary and possibly where code guidance was lacking. Finally, the unified collation of all available experimental information would form an extensive data base that could assist in identifying any major gaps in the spectrum of required experimental data and indicate where further research was necessary.