Yield Surfaces for I‐Sections with Bimoments

This paper presents the yield‐surface diagrams for an I‐section subjected to five active‐stress resultants, including the axial compression, two bending moments, torsion, and bimoment. The difficulties involved in establishing the five‐dimensional yield‐surface equations are circumvented through the adoption of a parametric approach. This approach treats an I‐section as the composition of three thin plates; i.e., one web and two flanges. The entire cross section is considered plastic only when all of its component plates become plastic, with one exception. One advantage to the present approach is that yielding of each component plate can be described by a two‐dimensional yield curve. In developing the yield‐surface diagrams for the I‐section, three yield patterns are identified. The results indicate that neglect of the bimoment effect will overestimate the plastic strength of the I‐section.