Cold-formed steel (CFS) sections are commonly used in modern roof construction. Most purlin members are of thin-walled open cross section. They are usually subjected to roof loading at the top flange in either an upward or a downward direction. The load application points, where the sheeting/purlin connections are located, are often eccentric to the shear centre, and thus inevitably generate a torsional moment that will induce twisting and/or warping deformations in addition to bending deflection. This type of complexity associated with the loading conditions will be exacerbated by the occurrence of single- or mixed-mode buckling (e.g. overall, distortional and local buckling) due to compression flanges tending to move sideways. The connections between purlin and roof sheeting provide a restraining effect on purlin members by preventing such lateral and twisting movements, and thus have a beneficial effect on their load-carrying capacity. In design practice, this effect should be taken into account from a design efficiency perspective. To this end, a key step is to quantify the rotational restraint stiffness by using an engineering-orientated model. This paper firstly reports a series of torsional restraint tests (F-tests) for both sigma and zed sections. Two loading directions were examined by adjusting the purlin fixing direction. The rotational angles between the connected flange and sheeting were recorded at each loading step, from which the moment–rotation curves were produced and presented for each test case. A linear relationship has been observed for the moment–rotation relationship from all test specimens. Secondly, a hand calculation model for calculating the rotational stiffness at each connection was developed. In that model, the rotation was deemed to be primarily caused by the localised deformation of the roof sheeting and the distortional deformation of the purlin flange. The rotation caused by the separation of connection was found to be negligible. The model was validated by the experimental test results and an example was presented to demonstrate the application of the model proposed. The rotational stiffness calculated by this model can be used to evaluate the input parameters required for numerical modelling of purlin– sheeting interaction.

Item Type:	Refereed Article
Keywords:	cold-formed steel, purlin, roof sheeting, rotational stiffness, connections, analytical method, experimental studies
Research Division:	Engineering
Research Group:	Civil Engineering
Research Field:	Structural Engineering
Objective Division:	Construction
Objective Group:	Construction Materials Performance and Processes
Objective Field:	Metals (e.g. Composites, Coatings, Bonding)
Author:	Chan, AHC (Professor Andrew Chan)
ID Code:	100999
Year Published:	2014
Web of Science® Times Cited:	12
Deposited By:	Office of the School of Engineering
Deposited On:	2015-06-05
Last Modified:	2017-11-06
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