Yield Surface for Thin Bars with Warping Restraint

Abstract

A procedure is described for deriving yield surface equations for thin‐walled open cross sections for cases in which Saint Venant torsion is small compared to warping torsion. The yield surface equations are expressed in terms of an axial force, bending moments in two planes, and the warping moment or bimoment. Equations are derived for the specific case of a Z‐section. These equations are shown to satisfy the uniqueness theorem of plastic analysis thereby furnishing the correct yield surface within the limits of validity of the assumptions made. The applicability and accuracy of the proposed equations are indicated.