Design of Cellular Members under Axial-Shear-Flexure Interaction

Due to lack of a design resistance for cellular beam-columns under the axial-shear-flexure interaction, the design interaction resistances were investigated through a validated finite element analysis. The beam-columns are simply supported and subjected to a mid-span point load and a compressive axial load, to provide the interaction. A modified interaction based on ANSI/AISC 360-16 and the shear design of SCI P355 were integrated to design the interaction resistance. In the parametric study of the interaction in various steel sections, the non-dimensional slenderness and opening parameters were examined. For beam-columns under high shear forces, Vierendeel mechanism and web-post buckling constitute the dominant failure modes depending on the opening parameters. Under high compression loads or flexural moment, flexural failure about the major axis is the dominant failure mode. However, the failure behaviors are generally combinations of the three modes. The design interactional resistance was examined in terms of failure shear forces computed from failure criteria of the three modes. Since design of the web-post buckling in SCI P355 does not consider effects of the interaction, their resistances are significantly higher than the FE results. The resistance is not governed by safety and requires modifications. On considering the co-existing actions in a quadratic interaction criterion, the proposed interaction resistance obviously complies with the FE results for cases of the web-post buckling failure, and agrees well with the FE results for cases of Vierendeel and flexural failure.