Cold-formed steel (CFS) built-up battened columns using Square Hollow Sections (SHS) offer promising potential for lightweight, high-strength structural applications. However, current design standards mainly address open-section configurations, leaving limited guidance for closed-section members. This study investigates the axial compression behavior of built-up battened columns fabricated from SHS, focusing on section thickness and batten spacing (300 mm and 400 mm). Six full-scale specimens were tested under axial loading to evaluate load-carrying capacity, failure modes, and lateral stability. Results show that built-up battened columns significantly outperform single SHS columns, with enhanced strength and improved resistance to global and local buckling. Closer batten spacing consistently yielded higher axial capacity and more ductile failure behavior, while wider spacing led to reduced performance and premature batten plate detachment. Failure mechanisms ranged from global buckling in single columns to combined local and flexural buckling in built-up specimens. The built-up column S3-H2-B300 achieved a peak axial load of 263.95 kN, outperforming single SHS column S2-H2-SHS (34.55 kN) by over 300%. Experimental-to-theoretical ratios ranged from 0.6 to 1.3, validating EN 1993-1-1:2005 with a mean ratio of 1.0. The findings support future design improvements for closed-section CFS battened columns, which differ from conventional shapes due to unique stiffness characteristics and buckling behavior. Limitations include fabrication imperfections and connection variability, which may influence buckling performance.
