Direct Strength Design of Cold-Formed Purlins

Abstract

The Limit States Australian/New Zealand Standard AS/NZS 4600:2005 and the North American Specification (NAS) for the Design of Cold-Formed Steel Structural Members 2001 (2004 Supplement) include the newly developed direct strength method of design (DSM). In both standards, the method presented (Chapter 7 of AS/NZS 4600:2005, Appendix 1 of NAS) is limited to pure compression and pure bending. The situation of combined bending and shear as occurs in a continuous purlin system is not considered. In order to extend the DSM to purlin systems, it is necessary to prescribe and calibrate a method for combined bending and shear. Eight different test series on purlin sheeting systems with single, double, and triple spans and both uplift and downwards load cases as well as screw and concealed sheeting have been performed at the University of Sydney over a 10-year period. As many of these tests consisted of continuous lapped purlins where combined bending and shear occurred at the purlin section just outside the end of the lap, it is possible to use these test data to propose an extension to the DSM. Furthermore, calibration of the proposals using the limit states design methodology is included in the paper. This paper makes two proposals for combined bending and shear, and calibrates them both for the full sets of vacuum rig test data.