Effect of Column Base Connections on the Stability of CFS Storage Rack Frames

The rapid expansion of the storage industry has made cold-formed steel pallet racks the preferred solution for high-density warehousing. Due to the high slenderness of rack frames in the down-aisle direction, even moderate variations in baseplate stiffness can significantly affect global stability. However, current design specifications provide limited guidance on modeling semi-rigid baseplate-to-upright connections, potentially leading to conservative or even unsafe designs. This paper investigates the effect of the column base restraint on the stability of unbraced irregular steel storage rack frames through nonlinear finite element analysis, in which the baseplate stiffness values are varied. Six baseplate stiffness conditions (pinned, rigid, three analytical formulations from the literature, and an experimentally obtained moment–rotation curve) were combined with three load distributions, resulting in eighteen rack models. The results show that the load distribution significantly affects both the load-carrying capacity and the benefit provided by the baseplate stiffness. For the more uniform load distribution, a larger number of columns contributed to the resisting mechanism near collapse, resulting in an average load-carrying capacity 47.45% higher than that obtained for the most unfavorable non-uniform loading condition. Comparative analysis reveals that base joint restraint conditions have a substantial impact on the frame’s ultimate load capacity and lateral displacement. The models with rigid bases presented load-carrying capacities on average 39.32% higher, and lateral displacements approximately three times smaller than those with pinned bases. In all models, collapse was governed by flexural-torsional buckling of the columns between the base and the first beam level; local and distortional buckling were outside the scope of the numerical model. Furthermore, the analyses revealed a threshold stiffness beyond which the connection effectively behaves as rigid, with no significant gain in capacity. The semi-rigid behavior of the baseplate connection is shown to be non-negligible and must be considered in design to achieve accurate and reliable stability predictions of cold-formed steel pallet racks. Finally, findings highlight the need for further investigation into the baseplate behavior, particularly regarding the variation of its stiffness with the compressive force in the upright.