Experimental Investigation and Direct Strength Design of High Strength Complex C-Sections in Pure Bending (No. R925)

Abstract

Plain C or Z-sections are two of the most common cold-formed steel shapes in use throughout the world. Other shapes are high strength SupaCee® and SupaZed® steel sections which are widely used in Australia as purlins in roof and wall systems. They contain additional return lips and web stiffeners which enhance the bending capacity of the sections. Design methods for these sections are normally specified in the Australian/New Zealand Standard for Cold-Formed Steel Structures (AS/NZS 4600:2005) or the North American Specification for Cold-Formed Steel Structural Members (NAS S100-2007). In both Standards, which include the newly developed Direct Strength Method of design (DSM), the method presented (Chapter 7 of AS/NZS 4600:2005, Appendix 1 of NAS) is developed for beams and columns, including the reliability of the method. This report presents two different test series on both plain C- and SupaCee® sections in pure bending. They were performed at the University of Sydney for the extension of the DSM to include channel section beams with complex stiffeners. Two different section depths and three different thicknesses of high strength lipped channel sections were tested in pure bending. Tests with and without torsion/distortion restraint straps screwed on the top flanges in the pure bending region were also considered to allow local and distortional buckling to form in the sections respectively. Test results and formulae developed from the DSM are summarized in the report. Three different cases where moments are used in association with yield, inelastic or plastic criteria in the DSM local and distortional strength equations are compared with the test data. By comparisons between cases, a proposed recommendation for DSM inelastic buckling strength design in pure bending with extended non-dimensional slenderness limit for both local and distortional buckling is given in the report.