Recent research into thin-walled ferritic stainless steel profiles

Although stainless steel offers a wide variety of interesting and valuable properties such as fire resistance and durability, it has not been commonly used in structural applications. This is changing however as recent years have seen an increase in the use of structural stainless steel, mainly owing to its aesthetic and architectural qualities. A number of similarities exist between stainless steel and typical carbon steel but there are sufficient differences to necessitate specific treatment in design standards for stainless steel, focused on structural applications. Austenitic stainless steels have been broadly studied in recent years but less information is available regarding the ferritic grades. This is despite the fact that ferritic grades have low nickel content resulting in a more cost-stable and economic material compared with austenitic stainless steel. Nevertheless, recent projects have highlighted some of the main features of ferritics. This paper summarizes the outcomes of several studies carried out at the University of Liège on cold-formed stainless steel profiles and also research currently underway at The Steel Construction Institute on ferritic stainless steels. Firstly, the material behavior of Grade 1.4003 is explained. A new method of evaluating the actual mechanical properties in the walls of cold-formed sections is proposed, which is not restricted to a single alloy or type of cross-section. The formulation is established and validated against experimental results. It is also compared to predictive models from various other authors. Secondly, experiments on cold-formed stainless steel lipped channel section columns are described. The profiles failed by combined distortional and overall flexural-torsional buckling. These tests were used to calibrate finite element models and, once verified against the test results, these models were used to generate additional results when necessary. Current design standards were then used to calculate the strength and the results were compared to the tests. On the basis of the conclusions drawn from these analyses, a new Direct Strength Method which takes account of this failure mode has been proposed. Finally, a state-of-the-art discussion is provided based upon the findings of the ongoing RFCS project “Structural Applications of Ferritic Stainless Steel”. In addition, future fire testing of stainless steel columns will be presented.