Strain-Based Design Model for FRP-Confined Concrete Columns

Synopsis: A constitutive strain-based confinement model is developed herein for circular concrete columns confined with fiber reinforced polymer (FRP) composites. A series of relationships were developed from experimental data, which facilitated the establishment of the strain-based model. The FRP-confined concrete constitutive model calculates the internal damage of the column by using the radial strain. The radial and axial strains at zero volumetric strain were used to mark the beginning of effective dilation response of the FRP composite jacket. The secant concrete modulus was used in the model and expressed as a function of the secant modulus softening rate, which depends on the ultimate radial to axial strain ratio. The experimental relationship for the ultimate radial to axial strain ratio is a function of the normalized effective confining stiffness. The secant modulus softening rate is constant throughout the plastic stress-strain response until failure. The FRP-confined concrete constitutive model evaluates the ultimate radial strain, which was related to the FRP composite effectiveness. The FRP-confined concrete model predicts the stress-strain response accurately for any normalized effective confinement stiffness.