Connections for structural cold-formed sections: Fid-Bau Portal

Connections for structural cold-formed sections

Goodwin, M.J. / Chung, K.F. / Griffiths, D.A.

Traditionally, cold-formed sections have been designed and produced by the manufacturers as proprietary products. However, there is strong evidence that designers would use cold-formed sections more widely in building construction to replace timber and to replace the lighter hot-rolled sections. Examples of the use of cold-formed sections could be in trusses, in secondary beams, and load-bearing walls as well as in prefabricated buildings. One of the major inhibitions to this wider usage is the lack of information and design guidance on connections between cold-formed sections. Many designers treat cold-formed sections in the same way as hot-rolled sections and use bolted connections with cleats or similar attachments. These forms of connection are unnecessarily expensive for lightly loaded members where other forms of connection may be more appropriate. However, there is little test data on fasteners other than bolts. The objectives of the research programme were to assess the range of connections presently used to join cold-formed sections and to identify those that could be further developed for common use. Standard lap shear tests and joint bending tests with different fasteners were carried out to examine the structural performance of the fastenings. Their usage and potential for site fixings were also assessed. Design values from BS5950: Part 5: 1987 and EC3: Part 1.3 (1993 draft) were also compared with the test results. These form the basic design data for fasteners to be used in connections between cold-formed sections. Different ways of mechanical enhancement in connections between cold-formed sections were also investigated. Lap shear tests with different forms of swaging around fasteners were carried out. With preformed swaging around bolts, tension fracture of the lap shear test specimens at the side of the holes can be achieved provided that the bearing resistance of the swaging is properly utilised. For effective enhancement of connection resistance, both the geometry of the swaging around fasteners and the clamping resistance of the fasteners are identified as important parameters. Practical connection configurations between cold-formed sections in buildings were also examined.