Abstract
The stability of hollow-section columns remains a central issue in structural engineering because they are widely used in buildings, bridges, industrial frames, and offshore systems. This study investigates the buckling resistance of square hollow section columns (SHS) made of S235, EN 1.4401/1.4404, and EN 1.4462 steels at ambient temperature and under elevated temperatures up to 800°C. A Eurocode-based analytical framework was employed to evaluate elastic buckling, plastic resistance, and buckling resistance for fixed-free members with varying cross-section size, thickness, and length. The results show that stainless steels retain a much larger proportion of their original resistance at elevated temperatures than S235 carbon steel. At 800°C, the mean normalized buckling resistance at elevated temperature to plastic resistance at ambient temperature was 2.56% for S235, 13.59% for EN 1.4401/1.4404, and 8.52% for EN 1.4462. Among the stainless steels studied, EN 1.4401/1.4404 exhibited the best normalized resistance retention at 800°C. The transition between elastic-buckling and plastic resistance dominated regimes was strongly influenced by both temperature and slenderness, with S235 exhibiting non-monotonic behavior due to the competing effects of stiffness degradation and strength loss, while stainless steels showed more gradual and favorable transitions.