Design Rules of Built‐Up Members in Load and Resistance Factor Design

Abstract

The AISC‐LRFD (American Institute of Steel Construction‐Load and Resistance Factor Design Specification for Structural Steel Buildings) Specification provides rules for design of built‐up members. The slenderness ratios of built‐up members that may buckle out‐of‐plane, say, about the Y‐Y axis for a two‐back‐toback‐angle member are discussed. Based on the LRFD equation (E4‐1) and the usual concept of the effective length factor, a modification of the slenderness ratios (Kl/r)m for built‐up members as given in the present LRFD Specification is proposed. The proposed formula with local effective length factor Km is concise, simple, and physically clear. It is consistent with the effective length factor recommended by the LRFD Specification, and has only one equation considering the effects of shear and connectors on buckling of built‐up members. The calculated results of the proposed formula are found to be in good agreement with available test results.