Experimental study and analysis of inner-stiffened cold-formed SHS steel stub columns

• The strength capacities of cold-formed SHS stub columns with relatively thick walls are investigated experimentally.
• In particular, the effect of stiffeners in such cases is evaluated.
• Numerical analysis is conducted to verify the FE model and supplement the experimental observations.
• The validity of extending code/standard methods usually applied for calculation of cold formed thin-walled members to the thicker wall cases is examined.

A series of axial compression tests was conducted to investigate the compressive behaviour of cold-formed steel stub columns with relatively thick walls (6 mm and 10 mm, respectively). Four different inner-stiffener arrangements were considered. Tensile coupons were cut from different parts of the square hollow section (SHS) sections to obtain a full picture of the enhanced material properties due to the cold-forming process. A finite element model was also developed and employed to provide a numerical perspective of the behaviour of the SHS columns. The applicability of two code-specified methods for the calculation of the strength of thin-walled cold-formed SHS columns for the present thick-walled cases is examined. The comparison shows that the AISI (and similarly AS/NZS) method tends to overestimate the sectional strength for the unstiffened and partially stiffened 6-mm thick columns, but predicts generally well (with slight underestimate) in the cases of well-stiffened 6-mm columns and all the 10-mm thick columns. The GB method, on the other hand, appears to predict well for all cases where the stiffening effect was less significant, but underestimates the sectional strength in the well-stiffened cases.