Compressive Strength of Axially Loaded Built-up Sigma Cold Formed Sections Columns
The use of cold formed steel sections in building constructions has lately seen rapid growth due to their light weight and easier erection. Generally, lipped channel sections are used more frequently .Sigma sections while requiring more effort in fabrication, they exhibit high strength to weight ratios compared with the lipped channel sections. This work presents experimental as well as numerical study of the strength of pinned-pinned axially loaded columns utilizing sigma sections. The column section consists of two back to back sigma cold formed sections. The two sections are connected through their webs with connecting fasteners. Eight specimens with variable plate element width to thickness ratio, and having different member slenderness ratios were tested. Residual stresses and geometrical imperfections were recorded. Moreover, the specimens were simulated by a nonlinear finite element model using four node isoparametric shell element that accounts for both geometric and material non-linearities. The measured geometric imperfections and residual stresses were included in the numerical model. The parameters studied include the properties of the cross-section such as the flange, web, and lip dimensions as well as the spacing of the web fasteners. Furthermore, several column heights are considered to study the different modes of failure. Finally, the results are compared with the ultimate strength predicted by the American AISI, the Eurocode-3 and DSM specifications. Results reflect that sectional (local/distortional) buckling governs the failure mode of short columns. Moreover, the AISI, the Eurocode-3 and DSM can reasonably predict the ultimate load capacity of such sections.