Distortional buckling capacity of Z-purlins through-fastened to metal panels under gravity loading

April 29, 2013
Publication: Structural Stability Research Council Annual Stability Conference, SSRC 2013, p 525-547
Author(s): Christopher Grey Graham Cranston Moen, C.D.

Abstract: The governing limit state for cold-formed steel purlins used in a metal building can be distortional buckling, where the compressed flange in contact with corrugated metal roof panels deforms in up-down half-waves along the length of the member. Current code equations for calculating distortional buckling capacity were derived experimentally with four-point bending tests; however, the controlling gravity load case for roof purlins can be snow or wind that may suppress these distortional buckling half-waves. This paper presents an experimental and computational study to explore and quantify the distortional buckling flexural capacity of metal building Zee purlins with and without through-fastened panels considering both four-point bending and a uniform pressure applied to the metal roof panels. A total of 12 tests were conducted on a typical metal building roof system employing a vacuum chamber, the results of which are compared to AISI Direct Strength Method capacity predictions. A thin-shell finite element modeling protocol for a metal building roof system, including contact effects and the individual screw fasteners, is presented and validated with the experiments. The protocol is used to study and explain the complicated distortional buckling panel-purlin interaction for the downward pressure load case.