Design of Angle Columns with Locally Unstable Legs (No. R830)

The report is concerned with angle section columns whose legs are slender and thus subject to local buckling in their ultimate limit state. For such slender angle sections, the local buckling mode is identical to the torsional mode and traditional design procedures become excessively conservative because they account for the torsional (local) buckling mode twice. The report describes design methods for slender equal angles which ignore torsion in determining the overall buckling stress and uses recently presented effective width equations to accurately determining the bending capacity of angle sections, as required in the beam-column design approach. The shift in the effective centroid resulting from local buckling is determined from the actual stress distribution, as obtained using Stowell’s classical solution, rather than the effective cross-section. Having validated the design procedure against tests on slender equal angles, the same procedure is applied to slender unequal angles. The columns are assumed to be simply supported and thus allowed to rotate about their principal axes