Axial Capacities of Eccentrically Loaded Equal-Leg Single Angles: Comparisons of Various Design Methods

For most structural engineers, the design of an eccentrically loaded single angle without lateral restraint along its length was considered to be a formidable task prior to the publication of the 2005 AISC Specification for Structural Steel Buildings. According to Section E5 of the 2005 Specification, the effects of eccentricity on single-angle members are permitted to be neglected by using the effective slenderness ratio as specified, provided that members are loaded at the ends in compression through the same leg; members are attached by welding or by a minimum of two-bolt connections; there are no intermediate transverse loads; the leg length ratio is less than 1.7, if angles are connected through the shorter leg; and the modified KL/r is less than or equal to 200. The 13th edition AISC Steel Construction Manual provided a design table (Table 4-12) of the available strengths in axial compression of eccentrically loaded single angles, with the assumption that the compressive force is applied at the geometric y-y axis at a distance of 0.75t from the back of the connected leg, where t is the angle thickness. Table 4-12 has been revised in the 14th edition AISC Steel Construction Manual. The new table corrects some numerical errors in the calculations and moves the compressive force to the midpoint of the connected leg. The values of the axial compressive design strength in Table 4-12 are developed on the basis of bending about the principal axes w-w and z-z.