Consideration of out-of-plane buckling in advanced analysis for planar steel frame design

Abstract

A technique that may be used to augment most in-plane advanced analysis procedures to account for inelastic out-of-plane flexural–torsional buckling in the design of planar steel frames is presented. The linear stability theory is adopted and the finite element analysis method is used to derive the second-order stiffness matrix. The effects of material nonlinearities and geometric imperfections on out-of-plane buckling strength are accounted for by substituting the elastic rigidities ( EI y , EC w and GJ) with their effective values, which are determined from calibrations against specification equations for member strength. Based on a set of attributes found in typical building frames, it is demonstrated that out-of-plane buckling is likely to govern the strength of nonsway frames and may control the strength of sway frames. Thus, the proposed advanced analysis technique is recommended for the design of both types of planar steel frames.