Second-order analysis for semirigid steel frame design

This paper presents an analysis method in which both the nonlinear rotational behaviour of beam-to-column connections and second-order (P-Delta and P-delta) effects of beam-column members are explicitly taken into account. By adopting the concept of an end-fixity factor, the proposed method is comprehensive regardless of the end rotational conditions of beam-column members and applies to frames with any combination of pinned, semirigid and rigid beam-to-column connections. In addition, the end-fixity factor simplifies the analysis procedure for semirigid frames. More importantly, the end-fixity factor may be valuable to the design of such structures because it provides a physical interpretation of the extent of rigidity available in a connection. Thus, it provides a convenient way for designers to compare the structural responses of a semirigid member to that of a rigid one. Examples are presented to demonstrate the validity and efficiency of the proposed approach. With only minor modifications, the proposed method is readily implemented in existing rigid frame analysis and design computer programs.