Design Interaction Equation for Steel Beam‐Columns

Abstract

For designing steel beam‐columns, the present AISC‐LRFD, AISC‐ASD linear interaction equations are simple to use, but they have some weaknesses. The AISC‐ASD interaction equations have a jump from a long to a short member, i.e., for a very short member, the stability interaction equation does not always reduce to the strength equation. For short beam‐columns in which the weakaxis bending and axial force are dominant, and for double curvature bending, the AISC‐LRFD bilinear interaction equation may result in an overly conservative design. In this paper, a unified design interaction equation for braced steel beam‐columns subjected to compression combined with biaxial bending is proposed. An extensive evaluation of the proposed design equation, as well as the AISC equations, is made and compared with exact inelastic solutions of I‐section beam‐columns and with the results of 81 full‐scale tests of biaxially loaded beam‐columns of I‐section. It is found that the load‐carrying capacity of steel beam‐columns can be estimated simply and more accurately by the proposed unified design interaction equation.