Constitutive Model for Fiber-Reinforced Polymer and Tie-Confined Concrete

The fiber-reinforced polymer (FRP)-confined concrete model proposal by fib was enhanced to take into account the confining effect of the already-existing steel reinforcement when retrofitting a reinforced concrete (RC) column with FRP jacketing. To this end, confining pressures contributed at each step of deformation by the case of existing transverse and longitudinal steel reinforcement were evaluated, considering the stress-strain law of the reinforcing steel. Moreover, the compatibility of strain in the lateral direction between the jacketing system and the encased concrete was enforced. Finally, the bilinear stress-strain response of FRP-confined concrete was terminated by jacket rupture, owing to hoop strains exceeding the strain capacity of the material or to interaction of the jacket with the buckled longitudinal bars. Correlation with three experimental studies was performed to validate the proposed iterative procedure.