Plastic behaviour of strengthened cold-formed steel section

Abstract

To date, the use of cold-formed steel on single storey industrial buildings particularly as structural element of a portal frame is restricted. Mostly, its application is as roof and wall framing, cladding, purlins and rails. Compared with hot-rolled steel, the use of cold-formed steel on a building has advantages such as light self-weight and corrosion-free problems, even though these are weaknesses to be overcome. The main problems are local buckling and low connection capacity. From the previous study, it was shown that cod-formed rectangular hollow portal frame using thick section indicated the plastic behaviour. This section is uneasy to be derived at site. Besides, some connection methods have also been suggested by previous researchers using bolts, rivets, press and weld but such the connections cannot reach rigid connection as needed for plastic design of portal frame. This research intends to study strengthening methods of cold-formed steel section and the connection performance improvement using cover plate. From this study, it is expected that cold-formed steel section can achieve plastic section and the rigid connection can be reached. The study was performed in two stages. In the first stage, the study on small cold-formed steel beams was done, while in the second stage, the study investigated a full scale of cold-formed steel beams and the connections. Specimens of this research consist of strengthened cold-formed closed beams and the moment connections. The beams are strengthened using a splice of hot rolled plate attached to the original section by screws and weld. The beams are in various design strength, thickness, screw spacing and number of web screw rows. Three types of connection i.e. welded, unbraced cover and braced cover connections were constructed for the specimens. Self-drilling screws for the section strengthening were applied on the connected members outside the cover plate. The experimental results were compared to the theoretical one. From this study, it can be concluded that the applied strengthening method significantly increase the moment capacity of the cold-formed steel sections. Similarly, the braced cover connection improves the connection to be rigid connection.