Simplified amplification factors representing material and geometric inelasticity in frame instability

An approach for assessing the inelastic, in-plane, collapse load of framed structures using amplification factors is extended to a broader range of material inelasticity. This manual method is based on the amplification factor approach for elastic, rectangular frames in the Canadian steel design code, but allows for material and geometric nonlinearity of both rectangular and non-rectangular frames on a consistent basis. Improved accuracy is achieved with a linear variation of the incremental amplification factor between a lower limit at the onset of inelastic behaviour and an upper limit at which plastic collapse occurs. A method is demonstrated for notionally separating the effects of material and geometric nonlinearity in experimental measurements or advanced finite element analyses. This is used for validating the proposed inelastic models for a steel frame and a reinforced concrete frame.