Prestressed cold-formed steel beams

A novel concept, whereby prestressing techniques are utilised to enhance the load-carrying capacity and serviceability performance of cold-formed steel beams, is proposed. The prestressing is applied by means of a high-strength steel cable located within the bottom hollow flange of the cold-formed steel beam at an eccentric location with respect to its strong geometric axis. Since the initial stresses generated by the prestressing are opposite in sign to those induced during the subsequent imposed vertical loading stage, the development of instabilities is delayed and thus the capacity of the cold-formed steel beam is enhanced. Owing to the pre-camber that is induced along the member during the prestressing stage and the contribution of the cable to the system bending stiffness, the overall vertical deflections of the member are reduced significantly. Prestressed cold-formed steel beams can provide highly-efficient structural solutions. Owing to their enhanced structural performance, for a given span and imposed vertical load, a smaller cross-section is required and thus a more lightweight solution is achievable. Potentially, the proposed beams can open up new applications for cold-formed steel in construction, particularly in cases where increased load-carrying capacities, longer spans and reduced deflections are desired. The current thesis presents the conceptual development of prestressed cold-formed steel beams. The mechanical behaviour of the proposed structural system is explored using analytical and numerical models with the origin of the obtained structural benefits being demonstrated. Finite element modelling is employed to simulate the behaviour of the proposed beams during the prestressing and imposed vertical loading stages and parametric studies are conducted to investigate the influence of the key controlling parameters, such as the prestress level, cable size, section slenderness and centroid location. Finally, design recommendations and failure criteria, which define the permissible design zone for the prestressed system, are developed with their implementation being demonstrated through practical a worked example. Open Access