Analytical Evaluation of FRP Wrapping Effectiveness in Restraining Reinforcement Bar Buckling

Abstract

Internal transverse steel reinforcements (e.g., stirrups) are the main internal devices that prevent the longitudinal steel bar buckling, but in many existing reinforced concrete (RC) structures the amount and the spacing between steel stirrups are inadequate. In these structures, longitudinal bar buckling can be prevented by applying external reinforcement, in particular, by means of fiber-reinforced polymer (FRP) wrapping. A novel analytical approach for the study of longitudinal bar buckling in columns wrapped with FRP is proposed. Longitudinal bars have been considered as axially loaded beams, whereas the mechanical effect of FRP wrapping on the bars has been modeled by means of springs. The effect of elastic and inelastic behavior has been taken into account by means of the reduced modulus theory. The well-known relations for steel stirrups have been revisited in the case of FRP wrapping to propose an analytical formulation, valid both for circular and noncircular cross sections of columns, for the evaluation of the FRP thickness needed to prevent the longitudinal bar buckling.