Investigation on Structural Behaviour of Cold-formed Steel Built-up Columns - Modified Direct Strength Method

An investigation of the behavior of cold-formed steel (CFS) built-up I column assemblies are presented. To study the interactive buckling mode of failures, the built-up column assembly failure modes and test results from the literature are collected, totaling 813 data points. The parameters including different shapes dimensions, lengths, spacing between the fastener connections, and slendernesses are investigated. The result shows that the local buckling deformations caused the built-up shape assembly columns to fail predominantly in interactive local and flexural-torsional buckling. The effect of spacing between the fastener connections and boundary conditions is also prevalent in the failure modes. The appropriateness of the AISI’s maximum intermediate connection spacing limitation is verified to prevent instability failures. The design results assessment indicated that the current AISI’s DSM design curve for interactive buckling is unconservative for the CFS built-up columns with predominant interactive local and overall buckling failure mode vulnerability.