Interaction Formulae for N‐My and N‐Mz and their Accuracy in Hollow Sections

In those cases where architectural requirements are a priority, hollow sections are the preferred solution. Considering cross‐sectional classes 1 and 2, plastic cross‐sectional design is a possibility that is preferable for both economic and ecological reasons. In technical standards and the literature, a wide variety of interaction formulae can be found. However, in most cases, information about their accuracy is not provided. In this article, the accuracy of the different interaction formulae for two frequently used combinations of internal forces and moments (N‐M_y and N‐M_z) is determined. Comprehensive parametric studies show that the interaction formulae for hollow sections given in EN 1993‐1‐1 exhibit some non‐conservative results. In addition to the comparison of the different accuracy levels, simplified interaction formulae will be introduced here allowing conservative plastic design of hollow sections.