Ductility of Reinforced Concrete Members Externally Wrapped with Fiber-Reinforced Polymer Sheets

The effectiveness of external wrapping with fiber-reinforced polymer for enhancing the curvature ductility of lightly reinforced concrete members is investigated. Referring to members with circular transverse cross sections, the performances in terms of both strength and ductility capacities are analyzed, and the predictive reliability of two different recent constitutive models, available in the literature and able to take into account the softening behavior of confined concrete, is checked. A parameter characterizing the effectiveness of the confining wrapping is proposed, and characteristic values are suggested. Moreover, referring to ductility increases due to confinement effects, a comparison is made between the predictions obtained using the constitutive models and simple expressions given in recent codes. Parametric analyses carried out highlight the importance of a definition of the limits of validity of expressions given in the literature for estimation of ductility increases in order to avoid nonconservative assessment.