Interacted buckling failure of thin-walled irregular-shaped aluminum alloy column under axial compression

Interacted buckling behaviors and ultimate strength of thin-walled aluminum alloy columns with irregular-shaped cross section were studied using a verified Finite Element Model (FEM). Six interacted buckling failure modes were studied, which were: (1) the interaction of Local bucking and sectional Yielding (LY); (2) the interaction of Local and Global buckling (LG); (3) the interaction of Distortional buckling and sectional Yielding (DY); (4) the interaction of Distortional and Global buckling (DG); (5) the interaction of Local bucking, Distortional bucking and sectional Yielding (LDY or DLY); and (6) the interaction of Local, Distortional and Global buckling (LDG). The load-axial displacement curve, the deflection-axial displacement curve, the development of the axial stress at different positions in the section at mid-span, the out-of-plane displacement at failure along the column length and the axial stress distribution at failure across the section at mid-span were presented. The local buckling and distortional buckling were detected by the turning points on the load-axial displacement curves. The out-of-plane displacement along the column length at failure was used to illustrate the failure mode of the column. Ultimate strengths and failure modes of 174 columns failed by interacted buckling failure modes were investigated by both FEM and current design approaches. For the ultimate strength of the columns under DY failure mode, the results predicted by North American specification for the design of cold-formed steel structural members of American Iron and Steel Institute (AISI) were higher than FEM simulation results. The ultimate strength predicted by American Aluminum Design Manual (AA), Direct Strength Method (DSM), European Code (EN1999) and Chinese Design Specification for Aluminum Alloy Structures (GB50429) were lower than FEM simulation results, no matter what kind of failure modes the column encountered. Mean values of PAA/PFEA, PEC9/PFEA and PGB/PFEA were 0.81, 0.79 and 0.74. DSM could precisely predict the Global buckling (G), LG and DY failure modes. However, for the columns failed by LY, DG, LDY and LDG, they were LG, G, DY and LG when predicted by DSM, respectively. The applicability of DSM to thin-walled aluminum alloy columns with irregular-shaped cross section should be investigated further.