<![CDATA[This study examines the effect of constrained-axis torsional buckling on steel column with a lateral restraint applied to one flange at the column midspan. The column dimensions used are WF300 x 150 (L = 4000 mm), WF600 x 200 (L = 8000 mm), and WF300 x 300 (L = 12000 mm). The analysis was carried out using finite element analysis with S4R shell elements. Linear buckling analysis (LBA) and geometrically-materially nonlinear analysis with imperfections (GMNIA) with an initial imperfection of L/500 were performed. The results confirm that CATB governs the elastic buckling mode in all three models. Comparison with AISC 360-22 analytical predictions shows that the current provisions are conservative for compact sections (WF300×150 by 4.65% and WF300×300 by 15.91%) but unconservative for the deep slender-web section WF600×200 by 21.88%. PEEQ distributions reveal that CATB failure is predominantly governed by geometric nonlinearity rather than widespread material yielding across all models. An effective length modification factor k is proposed, with K elastic ≈ 1.33 and K inelastic range from 1.5 to 1.9, suggesting that the AISC effective length assumption of Lcz = L/2 underestimates the actual effective length by approximately 33%. These findings highlight a gap in the current AISC 360-22 CATB provisions for sections with slender webs and provide a basis for further parametric investigation.]]>
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