PRESTRESSED COLD-FORMED STEEL BEAMS – PARAMETRIC STUDIES AND DESIGN RECOMMENDATIONS
Nicolas Hadjipantelis, Leroy Gardner and M. Ahmer Wadee
Department of Civil and Environmental Engineering, Imperial College London, London, UK
Owing to their enhanced load-carrying and serviceability performances, prestressed cold-formed steel beams can potentially open up new applications within the construction industry. In the proposed concept, an eccentric prestressing force is applied to cold-formed steel beams by means of a cable that is housed within a bottom hollow flange. During prestressing, tensile stresses are induced within the top region of the beam, thus delaying the occurrence of local instabilities under subsequent vertical loading. Consequently, the moment capacity of the beam is enhanced. Furthermore, owing to the prestressing, a pre-camber is also induced along the member, thus decreasing the overall vertical deflections significantly. Following discussion of the mechanical behaviour of the proposed beams, design recommendations are developed by employing interaction equations alongside the Direct Strength Method. Subsequently, finite element (FE) analysis is employed to investigate the effects of the prestress level and the section slenderness of the steel beam on the benefits obtained from the prestressing process. The parametric FE results are then utilised to assess the design recommendations.
Beam-columns; cold-formed steel beams; finite element modelling; interaction equations; parametric studies; prestressing.