Distortional buckling of X‐joints made of square hollow cross‐section beams: theoretical energy‐based model

Abstract

Current design codes do not consider distortional buckling failure modes, which can occur in the chord member of a tubular X‐joint loaded axially by brace members. In this study the critical load for distortional buckling is established based on the energy method and a beam on elastic foundation (BEF) approach. In the theoretical model the capacity is created by elastic bending of the chord faces in their own planes and elastic bending of the cross‐section as a frame structure. The theoretical capacity of an X‐joint is compared with numerical results obtained from finite element analyses (FEAs). Some discrepancy was found between theoretical model and numerical analysis, with the theoretical model slightly underestimating the load‐carrying capacity. Experimental tests show that an X‐joint can be prone to distortional buckling failure mode. However, detailed scrutiny of distortional buckling failure in X‐joints is only legitimate for joints made of high‐strength steel (HSS), because other failure mechanisms are more critical when conventional steels are used. Nevertheless, designers of X‐joints with rectangular hollow section (RHS) members should be aware of this potential failure mode.