Simplified design expressions for cold-formed channel sections

This study is a summary of the investigations into the design of cold-formed steel sections manufactured from high-strength steels (HSS), made by the Technical Research Centre of Finland (VTT) during the years 1989 - 1993. The main purpose of the project has been to obtain test data and develop and simplify the design rules for HSS members. The first part of the publication gives examples of the different stability phenomena of channel sections. In addition to the stability of members, such as flexural, torsional-flexural and lateral buckling, also the local buckling of unstiffened and edge-stiffened plates is considered. The second part presents the simplified design expressions. The main principles are in accordance with Eurocode 3 Part 1.3, but many conservative simplifications are given. The third part compares the predicted resistances with the experimental values. The test programme covers concentric compression tests, bending tests, eccentric compression tests and support reaction tests. The total number of full-scale tests made by VTT is 89. The cold-rolled test sections are U, C and hat profiles with different lengths. The material and cross-section properties varied in yield stress from 400 to 670 N/mm2, material thickness of 4 - 7 mm and web height of 110 - 280 mm. In addition to VTT's results, in all 178 other tests are analyzed. These results concern usual thin-walled carbon steel sections. When all the test results are treated as a family of tests, statistical analyses show that the expressions give satisfactory accuracy for normal design, but in some cases the results are very conservative and more accurate methods are desired. The comparisons confirm that the yield strength or wall thickness has no significant effect on accuracy.