This study investigates the maximum usable strain and the progressive failure of FRP-confined
concrete. Ten FRP-confined concrete specimens were divided into two groups with different jacket
stiffness. One specimen in each group was tested until failure while the others were loaded to target
strains and then unloaded in order to monitor the residual strength of the concrete cores. At 1% axial
strain of FRP-confined concrete, the residual strength of the concrete cores were reduced more than 56%
compared to the reference specimens. Experimental results have shown that the maximum usable
strain of 1% is un-conservative for FRP-confined concrete. The residual strength of the column cores
is equal to the ordinate of the intersection between the unload curve and the unconfined concrete curve.
The maximum usable strain of FRP-confined concrete is not a constant. It depends on the unconfined
concrete strength and the jacket stiffness.