Design of Class 4 hollow structural section compression members

This paper presents a study on the CSA S16:19, AISC 360-16, and EN 1993-1-1 approaches to determine the nominal capacity (C-n) of Class 4 hollow structural section compression members. Class 3 limits and effective width (b(e)) equations are compared, and the effect of member slenderness (KL/r), width-(or diameter-)to-thickness ratio, and height-to-width (or aspect) ratio on the relative C-n predictions are evaluated. For Class 4 rectangular hollow sections, CSA S16:19 is shown to under-predict C-n by up to 34% relative to AISC 360-16. A more economical, yet still safe, method to calculate b(e) (and hence, C-n) is proposed. For Class 4 circular hollow sections, a new method to calculate C-n utilizing the "effective area method" is proposed. This new method removes the need for having an "effective yield stress method" in CSA S16 Clause 13.3.4.