Résumé
With the introduction of the Eurocodes, a new design philosophy for the design of cylindrical shells against buckling was made available to structural engineers in Europe: the “Overall Method”, which makes use of the so-called “Overall Slenderness” of the shell to determine the appropriate (local) buckling reduction factor. There is a certain similarity between this concept and the Direct Strength Method (DSM) used in North America for the design of thin-walled cross-sections: the “Overall Method” also makes use of the results of (numerical) linear buckling analyses (LBA) for the whole shell to determine the slenderness and consequently the buckling reduction factor. In the case of the “Overall Method”, the combined load case, which may lead to shear, hoop and axial stresses, is thereby considered in the LBA. The paper discusses the background and application of this method and complications arising in certain cases. In particular, the application of the Eurocode rules to the design of slender (“class 4”) cylindrical hollow sections (CHS) will be discussed. While generally suitable for the design of large diameter cylindrical shells (tanks, silos), the application of the rules to the design of locally slender CHS requires a significant amount of interpretation by the code user and is generally not very accurate. Due to the increased use of (very) high strength steel grades for hollow sections in Europe (with yield strengths of fy=770 MPa and beyond), the local buckling design of HS steel CHS is becoming increasingly relevant. First steps by the authors towards the development of DSM-like design rules for high strength steel CHS under combined load cases will be discussed.