Numerical Studies on the Composite Action and Buckling Behavior of Built-Up Cold-Formed Steel Columns

An exploratory study is performed herein on the global, local, and distortional buckling behavior of built-up cold-formed steel members constructed using industry standard lipped channel sections. The stability characteristics of these columns under concentric axial compressive loads offers insights on member assembly (e.g. fastener spacing), and on the prediction of buckling loads (e.g., section rigidities) used in design formulations. Currently, built-up column buckling is determined using a modified flexural slenderness ratio, which reduces the buckling capacity in part due to a loss of shear rigidity in the overall member’s interconnections. In this paper, a numerical study is performed to analyze the level of composite action that can be achieved with idealized standard details, and which can then be used subsequently to more accurately predict the composite member strength. A parametric study using elastic buckling analysis was conducted on a representative population of built-up structural columns in ABAQUS. Member cross-sections, fastener spacing, and fastener grouping at the column ends were varied. Notable outputs include elastic buckling loads and column critical slenderness ratios. Buckling loads from the study are compared to code-based equation predictions and show considerable composite action, which can increase a column’s buckling load by up to 85% from its non-composite lower bound, assuming discrete connections. Future work includes experimental testing, nonlinear collapse simulations, and the development of new design formulations