“…Similar behavior was reported from compression tests on rectangular concrete specimens wrapped with small amounts of FRP: the specimens showed softening after maximum strength, while increasing strength in the second branch was observed for relatively high amounts of FRP [e.g., Karabinis and Rousakis, 2003]. Looking at the global behavior of FRP-retrofitted hollow piers, Mo et al [2004] found good agreement between experimental and analytical results, assuming in the analytical calculations a concrete law similar to the one depicted in Figure 5. In particular, a confined-concrete law that considers an increased initial stiffness and strength compared to unconfined concrete and comprises a softening post-peak branch until a residual strength, was found to accurately simulate the experimental force-displacement behavior of a set of eight piers with a 0.5 × 0.5 m hollow The numerical results are further discussed with focus on characteristic values of the stress-strain curves, namely compressive, f cc , and residual strength, f cr , strain at peak stress, e cc , and softening stiffness.…”