The capacity of rectangular hollow section (RHS) cold-formed stub columns with two opposing central circular openings
at column mid-height was experimentally studied in this research. The selected stub columns had a minimum yield strength of 357
MPa. The impact of two opposing central circular openings on the structural performance of tubular steel stub columns was
examined for perforation size to flat-width ratios of 0.4 and 0.6. Also, these columns with openings were strengthened with a doubler
plate. This study presents the ultimate column abilities, load-end shortening curves, regional geometric faults, and typical failure
modes extracted from the current test program. Further, this paper has presented a study of the potential of strengthening the RHS
stub columns by using external doubler plates with two distinct heights with doubling and tripling the aperture diameter. As for the
cold-formed thin-walled steel stub column strengthened with external doubler plates, the larger the doubler plate height, the greater
the improvement of the load ability. The ultimate buckling load capacity of the strengthened perforated rectangular hollow section
(RHS) under axial compression is increased by up to 40%.