An experimental study into flexural behaviour of sigma purlins attached with roof sheets

Abstract

Purlins made of cold-formed steel (CFS) sections are normally susceptible to failure caused by buckling due to their small wall thickness. Roof sheets, once attached to purlins with mechanical fasteners, will change the structural behaviours of purlin and produce beneficial effects by providing lateral or rotational restraints. In order to utilize these benefits, the interaction between purlins and roof sheeting needs to be considered in the purlin design. A number of research studies have been carried out on the behaviour of purlin-sheeting interaction. However, these investigations are mostly focused on purlins connected to sheeting with relatively small screw spacing, i.e. less than 300mm. In engineering practice, screws are often applied at every other trough of roof sheeting to save installation time, which leads to the screw spacing usually exceeding 300mm. Questions of whether and how the large screw spacing will affect the behaviour of purlins have not been specially addressed in any published literatures. This paper presents a detailed experimental study with the aim to answer these questions. A range of 27 CFS sigma purlins were connected to roof sheeting with screws applied at every other trough, as is adopted in installation practice, and were then subjected to both downward and uplift loading tests. From these tests, structural behaviours of purlin, i.e. the flexural stiffness, failure modes and the ultimate load, were examined, respectively. Test results are then used to develop design proposals for the sigma purlin that most codes or standards have not yet covered. This work is the first one that experimentally investigates sheeted sigma purlins subjected to both downward and uplift loads and considers screw spacing.