CFRP jackets prevented buckling of longitudinal bars and
maintained the dual confinement effect provided together with
internal transverse bars, as well as preventing spalling of cover
concrete. Therefore, the contribution of cover concrete to axial
strength and the contribution of longitudinal reinforcement to the
axial strength and ductility were maintained until very large axial
deformations, making the specimens benefit from the strain hardening
of longitudinal bars at the ultimate state.