DESIGN OF THIN-WALLED COLUMNS WITH UNSTIFFENED FLANGES

The compression member rules of the American Iron and Steel Institute, load and resistance factor design (AISI LRFD) Specification are investigated. It is shown that it is not necessary to limit the axial capacity of channel, single angle and Z-section columns with unstiffened flanges to the load causing local buckling of the flanges, as is required in the AISI Specification. Rules are proposed which greatly improve the AISI rules for concentrically and eccentrically loaded channel section columns with unstiffened flanges. The proposed rules allow the local buckling coefficient of the unstiffened flanges in bending to be determined on the basis of a rational buckling analysis when bending causes compression at the free edge of the unstiffened flanges. When bending causes tension at the free edge of the flanges, the proposed rules allow the flanges to be treated as stiffened elements.