Experimental and Numerical Gravity Load Performance of Stud and Bearer Sections in Cold-Formed Steel Panelised Construction

Cold-formed steel (CFS) panelised modern methods of construction can potentially help to mitigate the world's housing deficit and construction-related sustainability targets. Most existing research studied the global behaviour of bare or sheathed CFS wall panels under lateral or seismic loading instead of vertical or gravity loading. The efficient design of CFS panelised buildings under gravity loading is possible only when the behaviour of individual structural components can be precisely predicted. However, the design and numerical modeling guidance of individual CFS structural components acting as the critical gravity load-bearing components in CFS panelised buildings is restricted to ideal conditions instead of practical loading, restraint, and boundary conditions. As a result, there is a lack of design and numerical modeling guidance, causing their uptake to be lesser in the construction industry than necessary and highlighting the need for further research and development. Practitioners and Eurocode 3 follow the 'all-steel' design as sheathing may be damaged and replaced at some stage. Therefore, this thesis applied actual gravity load conditions and restraint arising from practical situations or boundary conditions to propose 'all-steel' design guidance and numerical modeling guidance for the efficient design of bare CFS lipped channel studs and unlipped channel bearer sections, the two critical gravity load-bearing structural components in CFS panelised construction. This research experimentally studied a total of fifty-six industry-standard bare CFS studs under monotonic, static vertical, or gravity loading scenarios and demonstrated that the track-boundary condition (BCT), which the studs are subjected to in CFS wall panels significantly influences the studs' axial compressive performance and failure mechanism under gravity loading compared to the ideal hinged boundary conditions (BCH). The studs' failure mechanism was flexural-torsional under BCT but flexural under BCH. Studs exhibited a two-phased axial stiffness due to the stud-to-track gap in BCT instead of a single axial stiffness in BCH. The studs' axial stiffness in BCT post-stud-to-track gap closure was 30% lower than BCH. An optimal effective length factor of 0.65 was suggested, considering the tracks' restraint stiffness for the efficient design of studs with BCT. No numerical modeling guidance exists in the literature that can precisely replicate the effect of BCT on the axial-compressive strength and stiffness behaviour of the CFS studs under vertical or gravity loading scenarios. This research addresses this gap by investigating softened pressure-overclosure relationships for the first time to propose a new FEA contact modeling approach for axially loaded bare CFS studs that can accurately predict the strength, stiffness, failure mechanism, and post-peak behaviour with BCT under gravity loading scenarios. New predictive equations were developed to determine the accurate softened contact parameters for the bare studs and to enable designers to use accurately calibrated models to capture bare studs' complex axial compressive behaviour in the elastic and inelastic range. For the first time, the combined web-crippling and bending behaviour of CFS unlipped channel bearer sections in load-bearing CFS panelised constructions were investigated through with lateral restraints and simply supported boundary conditions under single stud (Case I), double studs (Case II), and three studs/single panel (Case III) removal scenarios. Five different web-crippling equations in literature and web-crippling-bending interaction equations in Eurocode 3 and AISI S100 were evaluated with the test/FEA data. New characteristic nominal web-crippling-bending interaction ratios and modification factors to prescribed nominal web-crippling capacities were proposed for the bearers' efficient design under gravity loading and real-world stud(s) or single-panel removal scenarios.