Prediction of Immediate Deflection and Flexural Capacity of Unbonded Posttensioned Concrete Members Strengthened with External FRP Composites

Existing codes and design guidelines do not provide a procedure to compute the immediate deflection of unbonded posttensioned members strengthened with fiber-reinforced polymer (FRP) composites. The existing procedures are only applicable to unstrengthened reinforced or bonded prestressed concrete members. By incorporating the area of FRP sheets and the slip of unbonded prestressing steel, a general analysis approach based on equilibrium and strain compatibility is established to reproduce the experimental results of unbonded posttensioned members strengthened with FRP composites at service. The analysis used data from 16 tested specimens with different reinforcement ratios and FRP schemes. Calculation of deflection with the proposed modified expression of the cracked moment of inertia Icr is verified to predict the immediate deflection of unbonded posttensioned members strengthened with FRP composites when introduced in the two equations of the effective moment of inertia Ie, as recommended in the American code of practice for unstrengthened reinforced or prestressed concrete members. A satisfactory correlation of the load–deflection response is observed between the experimental and proposed approach. Finally, a validation of the proposed approach with other researchers’ work is performed by considering additional variables.