Imparting Ductility to FRP-Reinforced Concrete Beams Through Compression Zone Confinement

In recent decades, fiber-reinforced polymer (FRP) bar-reinforced concrete (FRP-RC) beams have attracted considerable attention as a corrosion-free beam form. However, FRP-RC beams have limited practical applications owing to their much lower ductility compared to conventional steel bar-reinforced concrete (steel-RC) beams. To improve the ductility of FRP-RC beams, this study presents an innovative sectional form for FRP-RC beams in which the compression zone concrete is confined with FRP spirals/hoops. With such a sectional form, the ductility of the beam is derived from the ductile behavior of confined concrete in the compression zone instead of the ductile behavior of steel yielding in a conventional steel-RC beam. An experimental program consisting of eight large-scale FRP-RC beams was conducted to validate the effectiveness of this sectional form, in which the variables investigated include the pitch of the FRP spiral used to offer confinement, amount of longitudinal tension FRP bars, and FRP confinement configuration. The test results demonstrate the effectiveness of FRP confinement in improving the ductility and load-carrying capacity of FRP-RC beams; for one of the beams tested in the present study, ductility was increased by 150% with only a corresponding cost increase of around 7%. The significant effects of design parameters on the behavior of such FRP-RC beams are clearly revealed. Finally, a finite element model for such FRP-RC beams was established and verified using the test results.