Passive confinement provided by fiber-reinforced polymer (FRP) jackets increases the compressive strength and axial deformation capacity of concrete. This study explains a normalized confinement stiffness approach to quantify the strength and strain increase of FRP confined concrete using a previously proposed and most widely-used model for both active and passive confinement of concrete, and claims that these equations can still be used for FRP-confined concrete with very simple modifications. A comparison of the proposed model's
accuracy to American Concrete Institute guidelines was made using experimental results reported in the literature. The proposed modified model was shown to be quite effective in predicting the increased strength and strain values of FRP-confined concrete, and was also modified for FRP-confined hollow concrete cylinders.