Structural system design of steel frames by plastic hinge-notional force method

The plastic hinge method inherently assumes the elastic-perfectly plastic type of 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. The notional horizontal force is assumed to be proportional to gravity loads so that the stability of the frame can be assessed with improved accuracy. The present paper compares the strength and behaviors of simple portal frames between the plastic hinge-notional force analysis and the more exact analysis. The paper also shows that this design method is most practical and useful taking our current situation for available computing means into consideration.