Plastic hinge method inherently assumes the elastic-perfectly plastic momentcurvature relation which results in unconservative strength of the frame. A gradual spread of plasticity in members is not considered. To fill this lack and include the effects of initial imperfections, the fictitious (notional) horizontal force is applied. It is assumed to be proportional to the gravity loads so that the stability of the frame can be assessed with improved accuracy. The present paper compares the strength and behaviors of frames between the plastic hinge-notional force analysis and the more exact analysis and concludes that this design method is most practical and useful.
