This doctoral thesis presents a comprehensive study on cold-rolled aluminium portal frames composed of back-to-back lipped channel sections. The research included an extensive experimental program on full-scale portal frames and components, a numerical simulation part on finite element modelling, and finally a proposal development of the design for the cold-rolled aluminium frame systems. The primary aim is to explore the structural behaviour and ultimate strength through experiments and numerical analyses, leading to the development of proposed provisions for the design of cold-rolled aluminium portal frames using Advanced Analysis. The study also evaluates the applicability of the current standards to the design of cold-rolled aluminium portal frames. Towards observing the structural behaviour and determining the ultimate strength, a series of seven full-scale tests on two-bay single-span cold-rolled aluminium portal frame systems, having a size of 14 m long by 6.7 m high, were carried out. Various frame configurations were tested for both gravity loading and combined horizontal and gravity loading conditions. Separate tests were performed on the column base connection to quantify the flexural stiffnesses of the base connections about the column-major and -minor axes so that the semi-rigidity of the base connection used in the full-scale frame test was evaluated, and the effects of different base brackets on the column base stiffness were also examined. Other laboratory experiments, including coupon and point fastener connection tests, were also conducted to obtain the necessary information on material properties, connection characteristics. Further, initial geometric imperfections of both members and systems were thoroughly measured for use in further numerical investigations. Nonlinear finite element simulations using shell elements and advanced analysis of the full-scale frames and the base connections were developed and calibrated against experimental results. All sources of major nonlinear actions, notably geometric, material, connector and contact nonlinearities, were included in the numerical finite element models. In details, the individual bolts used for the connections were simulated by deformable point-based fasteners. The force-deformation characteristics of the deformable fasteners, which were obtained from the point fastener connection tests, were incorporated and successfully implemented in the Advanced Analysis. Parametric studies were subsequently carried out on the basis of the calibrated modelling technique to determine the effect of the column base stiffness, as well as various configurations of the lateral bracing for columns, on the frame ultimate strength for both gravity load and a combination of horizontal load and gravity load. A larger span finite element model was also created to study the suitability of the frame design for larger spans. The strengths of cold-rolled aluminium portal frames were determined by the conventional methods available in the current international aluminium design standards/specifications and by the Direct Design Method using Advanced Analysis. A comparison of predicted strengths from the various design approaches was then performed. To account for inherent uncertainties in the strength of the cold-rolled aluminium portal frames, a system reliability analysis was conducted to derive system resistance factors. It was highlighted that the Direct Design Method using Advanced Analysis as proposed in this study is the robust and realistic method for the design of cold-rolled aluminium portal frames and is likely the future design method for all types of structures including those comprised of cold-rolled aluminium sections.