Presented in this thesis are the results from two distinct investigations on the behaviour of lightweight framing systems for buildings. One investigation concerns the characterisation of cold-formed steel sections of novel shape for the design of columns in modular construction, and this is reported in the first part of thesis. The second new investigation is for a theoretical analysis to determine the elastic critical buckling load for shear-flexible frames of fibre reinforced polymer sections. This work is detailed in the second part to the thesis. Modular 2000 Ltd. fabricated the column specimens that were characterized for the research on lightweight steel modular construction. To determine the reSistance of nine different column types a series of nominal concentric strength tests were conducted on specimens of 2.7 m length having a new E-section shape. The novelty to the shape is that it has no flat elements and is continuously curved in plan. Open E-sections are of S350 structural grade steel, are nominally 100x43 mm in plan, and have wall thicknesses of either 1.5 or 2 mm. Various bracket and enclosure combinations were the variables in the nine column types tested. These were connected to the E-sections by MIG plug-welding. Except for the 100x40x1.5 mm C-enclosure of S350, the other attachment components were of steel grade CR4, at 1.5 mm thickness. There were five column types with E-sections of 2.0 mm thickness and four with 1.5 mm thickness. Reported are the salient results from 54 strength tests, where the mode of failure was global buckling about the minor-axis of the E-column. To also determine the local buckling strength, and the effective area, a small series of stud column tests were performed on 200 mm long specimens of the 1.5 mm open E-section only. To support the understanding gained from the series of full-sized physical tests on E-columns, a programme of theoretical work is presented which is used to determine the design strengths of the column types and to predict the elastic and inelastic critical loads of a curved panel. Theory is also used to find a plasticity reduction factor for the E-section, which is required to "establish the effective area for local buckling. BS 5950-5: 1998 gives a code of practice for the design of cold-formed thin gauge sections. This current guidance is specific to steel sections comprising Simple shaped members that are of flat elements bounded either by free edges or by bends. The new results from the combined theoretical and eXperimental studies to characterise E-columns are evaluated and used to make recommendations on how SS 5950-5: 1998, and, in particular, Section 6 for members in compression, can be used with E-sections to design modular units. In the second part of the thesis the author shows how a static analysis for plane frames of shear-flexible members, written by a previous Warwick University PhD student, can be modified to calculate the elastic critical buckling load for overall instability. The modified sframe programme provides a practical analysis tool that, importantly, includes non-linearity by way of second-order P-L1 effects with shear-flexible functions and semi-rigid joint action. In conventional frame analysis shear-flexibility is ignored when members are of isotropic material (steel), and by way of a preliminary parametric study the author shows why the influence of shear deformation on reducing the buckling load of shear-flexible frames should not be neglected when the material is of fibre reinforced polymer. By studying the change in critical load in simple frame problems it is found that there is an interaction between shear-flexibility and the torsional stiffness given to the beam-to column joints. Moreover, the study on the instability of shear-flexible frames provides evidence to suggest that the relative stiffness values for joint classification boundaries are likely to be lower than those for steel frames by Eurocode 3 (BS EN 1993-1: 2005). This is an important finding for when a structural Eurocode or other code of practice is drafted for lightweight framed structures of fibre-reinforced polymer materials. Although the work presented in this thesis is from two distinct investigations the deliverables are important to the sustainable development of lightweight framing systems for buildings.

Reduced-activation ferritic steels are considered as the primary candidate materials for structural applications within nuclear fusion power plants. It is known that by mechanically alloying ferritic steel powder with Y (usually in the form of Y₂O₃) then consolidating the material by hot isostatic pressing, a nanoscale dispersion of oxygen rich nanoclusters as small as ~2nm is introduced into the microstructure. This vastly improves high temperature strength and creep resistance, and the nanoclusters also act as trapping sites for helium and point defects produced under irradiation. In this thesis, the evolution of the oxide nanoclusters in a Fe-14Cr-2W-0.3Ti & 0.3Y₂O₃ ODS alloy was investigated primarily using atom probe tomography. The microstructure was characterised at various points during processing to give an insight into the factors influencing the formation of the nanoclusters. It was found that the nanoclusters nucleated during the mechanical alloying stage, then followed near classical nucleation and growth mechanisms keeping the same composition of ~8%Y, ~12%Ti,~25%O and ~45%Cr throughout. The formation and evolution of 5-15nm grain boundary oxides was also observed, and these were shown to form first as Cr₂O₃ particles that subsequently transform into a Y-Ti-O based oxide on further processing. The influence of mechanical alloying with 0.5wt.%Fe₂Y rather than 0.3wt.%Y₂O₃ was also investigated, and this showed that there was no difference in the final microstructure produced provided the level of Ti in the starting powder was tightly controlled. Without sufficient Ti, the nanoclusters were Y-O based and ~6nm diameter. Both the Y-O and Y-Ti-O nanoclusters were moderately stable on annealing at 1200°C for up to 100 hours, with only minimal coarsening observed. Ti was found not to influence the coarsening rate of the nanoclusters significantly. The stability of the oxide nanoclusters under irradiation was investigated by using Fe²⁺ ion irradiation to simulate displacement cascade damage in the ODS-Eurofer material (the official European candidate material for testing in the ITER fusion test reactor). Doses up to ~6 dpa at 400°C were used, and there was no significant change to the nanocluster distribution. However segregation of Mn to dislocations was observed after irradiation. These results indicate that ODS steels are good candidate structural materials, as the microstructure is stable at high temperature and under irradiation. The starting powders, and processing parameters need to be tightly controlled in order to produce the optimal material for use in service.