Effect of stressed skin action on the behaviour of cold-formed steel portal frames with non-linear flexible joints and top-hat purlins

Previously held under moratorium from 1st December 2016 until 1st December 2021.A conceptual design of a cold-formed steel (CFS) portal frame system proposed by the industrial partner is to be investigated and improved in light of known design challenges. Unlike previous studies which focused on the behaviour of CFS bare frame, this thesis focuses on the design and analysis methods for clad portal frames. A wide range of design problems and industry practices have been investigated by testing, as follows:1) Resistance and stiffness of bolted moment-connections. The bearing resistance and stiffness of the threaded bolt shank in single and double shear lapped connections were tested and compared against design recommendations.The existing methods for deriving the moment resistance and the rotational stiffness of the moment-connections were updated for tested joint configurations 2) Shear resistance and stiffness of cladding panels. A total of eighteen 3 x 3 m cladding panels were tested including options in which sheeting is fixed on all four sides and fixed on two sides only. The design features not yet recognized by design codes such as top-hat purlins, sheeting profiles fixed in the crest, profile thickness less than 0.5mm and composite panels were investigated in the test programme. 3) The difference in the structural behaviour of the bare and clad portal frames. A series of six full-scale laboratory tests were conducted on cold-formed steel portal frame buildings in order to investigate the effects of joint flexibility and stressed skin diaphragm action. The frames used for the laboratory tests were of 6m span, 3m height, 10° pitch and the frame spacing was 3 m. When the difference in loads between 2D (bare frame model) and 3D (stressed skin model) were considered, it was shown that the resistances and flexibilities of frames and cladding should be calculated or established by testing so safe and economical design is possible.A conceptual design of a cold-formed steel (CFS) portal frame system proposed by the industrial partner is to be investigated and improved in light of known design challenges. Unlike previous studies which focused on the behaviour of CFS bare frame, this thesis focuses on the design and analysis methods for clad portal frames. A wide range of design problems and industry practices have been investigated by testing, as follows:1) Resistance and stiffness of bolted moment-connections. The bearing resistance and stiffness of the threaded bolt shank in single and double shear lapped connections were tested and compared against design recommendations.The existing methods for deriving the moment resistance and the rotational stiffness of the moment-connections were updated for tested joint configurations 2) Shear resistance and stiffness of cladding panels. A total of eighteen 3 x 3 m cladding panels were tested including options in which sheeting is fixed on all four sides and fixed on two sides only. The design features not yet recognized by design codes such as top-hat purlins, sheeting profiles fixed in the crest, profile thickness less than 0.5mm and composite panels were investigated in the test programme. 3) The difference in the structural behaviour of the bare and clad portal frames. A series of six full-scale laboratory tests were conducted on cold-formed steel portal frame buildings in order to investigate the effects of joint flexibility and stressed skin diaphragm action. The frames used for the laboratory tests were of 6m span, 3m height, 10° pitch and the frame spacing was 3 m. When the difference in loads between 2D (bare frame model) and 3D (stressed skin model) were considered, it was shown that the resistances and flexibilities of frames and cladding should be calculated or established by testing so safe and economical design is possible