Second-order analysis and design of imperfect composite beam–columns

In current practice, the design of composite columns such as concrete-filled and concrete-encased steel columns is a member-based procedure which is based on linear analysis in conjunction with the effective length method, rather than a system-based approach utilizing the concept of advanced analysis. In principle, the advanced analysis can be used for any structural forms when imperfections are considered and proper plastic functions for cross-sections are used. The new method considering these issues needs to be calibrated with design codes and experimental tests. Surprisingly, the application of advanced analysis to composite structures is relatively rare in the literature and the advantages have not been exploited fully. In this paper, an “advanced analysis” design method for composite columns is proposed, and the results predicted by the proposed method are compared with the results calculated by Eurocode 4 and from laboratory tests. With the verification and calibration carried out in this study, without loss of generality, the proposed method can be applied to the design of composite structures beyond the scope of the conventional design method and without the assumption of an uncertain effective length factor, which implies an improved accuracy and convenience, as frame classification for the use of the effective length method or alignment charts is no longer needed.