Nonlinear inelastic buckling of rigid-jointed frames under finite displacements

Summary A nonlinear analytical approach for establishing the precise load-carrying capacity of imperfection-sensitive frames, made from ideal elastic-plastic material, is presented. The imperfection sensitivity is due to support eccentricities of columns. Stability criteria for both modes of failure, due to elastic and inelastic buckling, are established. The failure through inelastic buckling occurs for frames exhibiting postbuckling strength or monotonically rising equilibrium paths. The inelastic analysis is approximate with a basic assumption that the overall response of the frame can be predicted by considering the elastoplastic stress distribution at only one single (the most unfavorable) cross-section. Plastic buckling is associated with a limit point instability. Simple formulas for evaluating the stress distribution at the critical sections in both the elastic and inelastic range are assessed. The proposed method is demonstrated by means of a simple two-bar frame for which the overall response from the onset of loading up to failure is determined.With 5 Figures