Design of perforated cold-formed steel hollow stub columns using direct strength method

This paper presents a numerical investigation on the performance and design of cold-formed steel square (SHSs) and rectangular hollow sections (RHSs) stub columns having two opposite central circular perforations located at column mid-height. Finite element (FE) models are initially developed and validated against the experimental results on perforated YSt-310 cold-formed steel stub columns reported by the authors. A total of 264 experimental and numerical column capacities, collected from previous experimental investigations and current parametric study, has been utilized to compare with the design strengths predicted by available codified and proposed design equations. Based on the analysis, most of the presently available design equations for perforated stub columns provide overly-conservative and highly scattered design predictions. In particular, the Direct Strength Method in American Standard provides the maximum overly conservative prediction of about 60% with high scatterings. Hence, a modified DSM design equation has been proposed for various perforation size ratios (i.e. diameter of perforation to flat element width) considering the previous test results and current FE column capacities through least square regression analysis. The newly proposed design equation is shown to offer improved mean (conservative) and reliable predictions, and therefore recommended for inclusion in future revisions of design codes for perforated cold-formed steel tubular stub columns.