An effective stress approach for the design of rectangular hollow section flexural members with slender elements

An evaluation of North American and European design provisions for rectangular hollow section (RHS) flexural members with slender elements is performed. Seventy-three non-linear finite element models, covering practical ranges of width-to-thickness, height-to-thickness, and aspect ratio are developed, validated, and analyzed. The results demonstrate that current Class 3 or non-compact limit(s) in CSA S16, AISC 360, and EN 1990 are accurate; however, the effective width methods used in the current nominal strength expressions are inconsistent across different RHS orientations, and conservative (up to 11 %). To address this, a new effective stress approach using gross-section properties was explored. The new approach is shown to increase (up to 9 %) the accuracy and precision of nominal strength predictions when compared to the current approach(es), for all orientations, and still meet/exceed target reliability indices based on an approximate first-order reliability method analysis.