This thesis describes an investigation of the shear buckling strength of thin metal plates and empty and filled Cold-Formed steel lipped C-shaped cassette sections without intermediate stiffeners in the longitudinal or in the transverse direction of the wide web of the cassettes for various boundary conditions, material properties and geometrical characteristics. Tests were carried out to determine the properties of the metal skin of the cassettes and of the three polystyrene foams that were used for the infilling of the liner trays. Experiments have been carried out on C-shaped cassettes when the wide flanges are stabilised by various lightweight insulation materials fixed in position. A range of alternative numerical analyses complements this experimental research. An extensive literature research has been carried out covering Thin Metal Plates, Cold-Formed Steel Sections, Diaphragms, Composites Structures, C-shaped panels, Sandwich Panels, Polystyrene and Polyurethane materials, and the effect of Intermediate Stiffeners in various cases. The background reading embraced all aspects of the design and behaviour of Cold-Formed steel sections and sheeting. Consideration was given to BS 5950: Part 5,1987 "Code of practice for design of cold formed sections", to the A1S1, 1986 "Design and analysis of cold. formed steel sections", and to Eurocode 3: Part 1.3, 1997 "Coldformed thin gauge members and sheeting". However, a more detailed study was concentrated on the shear buckling of stiffened and unstiffened thin-plates and G shaped panels with and without intermediate stiffeners.