Structural behaviour of composite cold-formed steel systems

The topic of this thesis is the investigation of the structural behaviour of cold-formed steel flooring and purlin systems, taking into consideration the beneficial effect of interaction between structural components. Experiments have been conducted on flooring systems comprising cold-formed steel joists and wood-based particle boards, considering the typical screw fixings employed in current practice as well as alternative means of shear connection. The experimental findings showed that mobilisation of composite action within this type of system, through enhancement, beyond that currently used, of the employed shear connection, is feasible, bringing corresponding increases in capacity and stiffness. In order for the influence of the key parameters to be further examined, a finite element model simulating the examined systems has been developed, validated and employed for parametric studies. Analyses confirmed the experimental findings, showing that significant benefits in terms of capacity and stiffness can be achieved, especially for systems comprising thinner steel sections. Based on the obtained experimental and numerical results, a full design method, following the fundamental concepts of current design codes for composite structures, has been devised, providing accurate predictions of moment capacity and flexural stiffness. Finally, a numerical investigation has been performed on continuous two-span roof systems comprising cold-formed steel purlins, accounting for their interaction with the corrugated sheeting. The study showed that moment redistribution is possible within these systems, but usually accompanied by a reduction of the moment capacity of the central support. A previously devised method for the design of continuous purlin systems, making direct use of cross-section capacities at key locations, together with a factor to allow for the fall-off in moment at the central support, has been assessed and advanced.