Allowable Stresses for Nonrectangular Sections Under Combined Axial and Bending Loads

Abstract

The design stress allowables for various loading conditions involving bending in Section III, Division 1 and Section VIII, Division 2 of the ASME Boiler and Pressure Vessel Code are based on the assumption of a rectangular cross section of the structural members. These allowables do not necessarily provide the same level of safety for all general cross sections. In this work, stress allowables have been proposed for design, level C and test condition loadings to provide adequate safety for all combinations of axial and bending loads. The limits are based on an in-depth study of the interaction curves for the fully plastic condition under combined axial and bending loads. These proposed limits are intended to replace the existing ones in the ASME Code. These modifications apply to the design, level C and testing limits. (NB-3221.3, NB-3224 and NB-3226) of Section III, Division 1, and to the Design and Testing limits (AD-140 and AD-151) of Section VIII, Division 2 of the ASME Code. The modified limits are based on the inclusion of shape factors of individual cross sections.