Inelastic instability of rectangular and nonrectangular frames

Abstract

Proposals are described for extending the elastic amplification approach to frame instability given in the Canadian and South African codes for structural steel design to both nonrectangular frames and material inelasticity. The proposed approach to generalized nonrectangular frames is based on sway equilibrium equations which are derived by the principle of virtual work for each independent mode of sway collapse. The influence of material inelasticity is assessed by idealizing the moment-curvature relationship and the load-deflection behaviour between an effective elastic limit and the formation of the plastic collapse mechanism. A number of examples are given which demonstrate both the simplicity and accuracy of the method.Key words: codes, design, frames, inelastic properties, plastic properties, stability.