Use of angle cleats to restrain cold-formed channels against lateral torsional instability

• All beams failed by catastrophic distortional buckling of the web and flange.
• Distortional buckling occurred after extensive lateral-torsional buckling.
• The modes of failure did not affect the restraining angle cleat.
• The two 12 mm diagonally aligned bolts generated enough rotational resistance.
• AISI S100-13 underestimates the strength for short unbraced length.

It is common practice in the steel construction industry to restrain members that largely in flexure and torsion using a combination of angle cleats, connected at the top flange, and fly-bracings. This system is complicated and expensive, especially when used to restrain channels in bending. This paper investigates experimentally the use of angle cleats, connected to the webs of both the purlin and the channels, as a restraining system. Pairs of channels were subjected to a two point loading system in order to simulate a distributed load. Variable in the tests include the unbraced length between the two-point loads and the size of the channels. Failure of the channels occurred by lateral torsional buckling and catastrophic distortional buckling of the intermediate unbraced length. Tests showed that the purlin-cleat restraining system is able to resist lateral torsional buckling of the channels, and that this system can be used without any fly bracing. Distortional buckling was the final failure mode, and it occurred at moments less than the predicted lateral-torsional buckling moment of resistance. Distortional buckling is more critical in frames with shorter unbraced lengths and thicker channels.