Experimental Investigation of High Strength Cold-Formed $C$ -Sections in Combined Bending and Shear

In roof systems, a high strength steel profiled sheeting fastened to high strength steel cold-formed purlins of a lipped $C$ - or $Z$ -section is commonly used throughout the world. The design of such systems is performed according to the provisions of the limit states Australia/New Zealand Standard for Cold-Formed Steel Structures in Australia and the North American Specification for the Design of Cold-Formed Steel Structural Members in the United States. In both standards, which include the newly developed direct strength method of design (DSM), the method presented is limited to pure compression and pure bending. The situations of pure shear and combined bending and shear as occurs in a continuous purlin system are not considered. In order to extend the DSM to purlin systems, three different test series on high strength cold-formed $C$ -section purlins have been performed at the University of Sydney. The test series include predominantly shear, combined bending and shear, and bending only test series. Two different section depths and three different thicknesses of the lipped channel section were tested in this study. Further, tests with and without torsion/distortion restraint straps screwed on the top flanges adjacent to the loading points were also considered. This paper summarizes the test results and formulas developed from the effective width method and the DSM. Proposals for design are included in this paper. Comparisons with the Australian Steel Structures Standard are also included to take account of the tension field action.