This study investigated the structural performance of built-up hollow sections – cold-formed rectangular hollow flange beams. These built-up sections were made of a single steel sheet or three steel sheets where spot-weld screw fastening and self-pierced rivet were used for the connections. Experimental study was performed to determine the reliable structural capacity of these built-up section columns of different element and member slendernesses. Thereafter, Finite Element (FE) models were developed and validated using the test results. FE analysis and test results were compared with the design rule predictions (AS 4100 and AS/NZS 4600), and suitable recommendations were proposed. New direct strength based design rules were also proposed.