Cold-formed steel portal frame joints: a review

This paper reviews research published on cold-formed steel portal joints, beginning with the laboratory tests of Baignent and Hancock (1982) and ending with those of Rhodes and Burns (2006). The moment-capacity of the cold-formed steel channel-sections being connected in the portal framing systems ranges from 3.6 kNm to 128.5 kNm, with each type of framing system employing a different joint detail. While in accordance with the Eurocode 3 joint classification system, the joints arrangements reported would be classified as semi-rigid, for the purpose of design the majority of the joints would be sufficiently rigid for the frames to be designed safely to the ultimate limit state using a rigid-joint assumption, with the joints capable of sustaining almost the full-moment capacity of the cold-formed steel channel-sections being connected. However, in order for the assumption of rigid joints to be valid, the number of bolts or specialist components required may, in some countries, result in the joints being uneconomical to fabricate. It is seen that of all the joints reviewed, the joint arrangement tested by Rhodes and Burns is distinctive as rigid-joints are formed inexpensively through the use of knee braces. This, however, is at the expense of losing clear height to the eaves. Using UK design practice, a parametric study of sixteen frames, having spans ranging from 8 m to 14 m, is described that compares the economy of rigid-jointed frames against that of knee-braced frames. It is shown that use of a knee-braced frame results in a 10% increase in load carrying capacity, and a 36% reduction in horizontal deflections.