Comparison of the General Method with the Overall Method for the out-of-plane stability of members with lateral restraints

Abstract The generalised slenderness concept has been gaining popularity recently. One of the methods that is based on this concept is the General Method, which was introduced in Part 1-1 of Eurocode 3 to enable the assessment of the out-of-plane stability of steel members that fall outside the scope of the buckling resistance of uniform members formulae. However, there is still uncertainty regarding the safety and accuracy of this method, namely when dealing with members that possess complex lateral restraints. The General Method resulted from an adaptation of a method present in Part 1-5 and Part 1-6 of Eurocode 3 that is commonly designated by the Overall Method, though it is not clear why this adaptation was performed. In this paper, a comparison between numerical results and results obtained by both methods, for members with different configurations of lateral restraints, is provided. The study shows that non-conservative results are obtained when applying the Overall Method to the more restrained cases, where the in-plane and out-of-plane buckling modes occur for almost the same load amplifier, while the General Method returns conservative results for the same cases. It is seen that when the in-plane buckling mode is the critical one, the assessment of the in-plane buckling resistance of the member would be sufficient to guarantee its safety. Additionally, this study provides insight into the problem of definition of imperfections when dealing with members with lateral restraints.