Strain-Based Confinement Model for FRP-Confined Concrete

A constitutive strain-based confinement model is developed for circular concrete columns confined with external fiber-reinforced polymer (FRP) composite jackets. The model includes the properties of the concrete microstructure through a series of relationships developed from experimental data and the fundamental stress-strain behavior of concrete. The secant concrete modulus was used in the model and expressed as a function of the secant modulus softening rate. In addition, the ultimate radial strain was related to the FRP composite effectiveness. The distinguishing feature of the model is that it includes the effects of FRP confinement on the concrete microstructure by evaluating the internal concrete damage using the axial, radial, and volumetric strains. The FRP-confined concrete model predicts the axial stress at any level of axial strain accurately for any normalized effective confinement stiffness of the FRP composite jacket as verified in comparisons with experiments.