Restraining bars buckling by means of FRP wrapping: an analytical approach

Internal transverse steel reinforcements (e.g. stirrups) are the main internal devices that avoid the longitudinal steel bars buckling, but in most of all existing RC structures the quantity and the spacing between steel stirrups are inadequate. In these structures longitudinal bars buckling can be avoided by applying external reinforcement, in particular, by means of Fibre Reinforced Polymer (FRP) wrapping. A novel analytical approach for the study of longitudinal bars buckling in column wrapped with FRP is proposed. longitudinal bars has been considered as axially loaded beam, while the mechanical effect of FRP wrapping on the bars has been modelled by means of springs. The effect of elastic and inelastic behaviour has been taken into account by means of the reduced modulus theory. The well-known relations for steel stirrups has been extended to the case of FRP wrapping to propose an analytical formulation, valid both for circular and noncircular column cross sections, for the evaluation of the FRP thickness needed to avoid the longitudinal bars buckling.