Plastic Design of Unbraced Multistory Steel Frames with Composite Beams

A method for the plastic design of unbraced multistory steel frames under combined permanent gravity loads and horizontal accidental loads due to wind or earthquake effects is described in Ref. 1. The method permits the designer to plot horizontal load-lateral displacement curves (Q-D curves) for one or more stories, corresponding to assumed preliminary sizes of beams and columns, considering the formation of successive plastic hinges and taking into account the PD effect. The characteristics of these curves and the sequence of formation of plastic hinges indicate whether the sizes assumed for beams and columns are adequate or not, and furnish the designer with information about the individual members whose modification would more likely contribute to obtain a satisfactory behavior. Final shapes are selected keeping in mind the convenience of having all plastic hinges forming in the beams.