According to Eurocode 9, cross-sections are classified into different behavioural classes depending on the width-to-thickness ratios of the plate elements constituting the member section. To this scope the plate elements are separately considered and the most severe class is assumed as the one governing the section behaviour against local buckling. The main criticism to this classification system is due to the fact that, while the behavioural features of the different classes are clearly identified, the limit values of the width-to-thickness ratios between two adjacent classes do not account for the mutual restraining conditions between the plate elements constituting the section.

In this paper, starting from the results of a wide experimental program devoted to the evaluation of the ultimate resistance and ductility of aluminium alloy members subjected to local buckling under uniform compression, a new classification system accounting for the interaction between the two slenderness parameters of the cross-section has been developed and proposed.