Strength requirements of single cold-formed channels connected back-to-back

Tests to determine the failure modes and capacity of the eaves region of steel portal frames are presented. This was part of a major research project to establish the overall behaviour of steel portal frames, constructed from single channels and bolted back-to-back at the eaves joint. Variables in the 4 tests include the number of bolts in the connection, the points of contraflexure, the width of the channel flanges and the strength of the channels. Three modes of failure were observed, namely: local buckling of the compression zone of the flange and web of the channels, lateral torsional buckling of the channels between points of lateral support, and bolts in bearing. The final failure mode in all structures was local buckling of the compression flange and web. Local buckling was made more critical by stress concentrations, shear lag and bearing deformations caused by back-to-back bolted connections. It is proposed to apply a factor of 0.8 to the yield moment and the buckling moment of resistance to account for stress concentrations, shear lag and bearing deformations.