Elastic critical buckling stress of flanged cruciform sections subjected to uniform moment

Abstract

Steel flanged cruciform sections (FCS) are primarily used in structural systems due to their attractiveness when designing for two-way action moment frames. Their usage is also becoming more popular as vertical load-bearing elements in high-rise structures due to each member's significant axial load resistance. The research on cruciform and flanged cruciform sections has been relatively limited, and their buckling behaviour has not necessarily been fully addressed. This dissertation explores further the behaviour of the flanged cruciform section when subjected to a uniform moment along the member length. This dissertation will theoretically examine the existing information currently available for designers, both in the form of technical literature as well as in Eurocode 3 EN 1993-1-1 (2005). They are compared to Finite Element critical buckling eigenvalue analyses using LUSAS (2021) for the family of flanged cruciform sections made of IPEA 100, 200, 300, 400, 500 & 600. The effect of initial imperfections in the elastic buckling behaviour of FCSs is also investigated. The FEA results show that flanged cruciform sections may buckle in a distortional or deformational torsional manner. The finite element analyses and theoretical equations derived from a mathematical approximation of the buckling phenomena are compared. This dissertation aims to provide guidelines for structural designers to estimate the elastic critical buckling stress for FCS subjected to equal and opposite end moments.