Eccentrically Loaded FRP Confined Concrete with Different Wrapping Schemes

This study presents the results of an experimental program on the comparative performance of fiber-reinforced polymer (FRP) confined concrete specimens with different wrapping schemes. A total of 32 specimens in four groups were cast and tested under concentric and eccentric axial loads. All specimens were wrapped with the same amount of FRP but with different wrapping schemes, including full wrapping, partial wrapping, and nonuniform wrapping. Specimens in the first group were fully wrapped (Group F). Specimens in the second group were partially wrapped with 30 mm FRP strip spacing (Group P30). Specimens in the third group were partially wrapped with 60 mm FRP strip spacing (Group P60). Specimens in the fourth group were nonuniformly wrapped with a combination of full and partial wrapping (Group FP). Two similar specimens in each group were tested under concentric, 15 mm eccentric, 25 mm eccentric, and 40 mm eccentric axial loads. The test results indicate that fully wrapped specimens outperformed other groups of specimens under both concentric and eccentric axial loads, which were followed by nonuniformly and partially wrapped specimens. With the increase in axial load eccentricity, the performance in all groups significantly decreased. Moreover, with the increase in axial load eccentricity, the failure mode changed from FRP rupture at the compression side to extensive concrete cracking at the tension side. Equations were developed to predict the compressive strength of FRP confined concrete with different wrapping schemes. Experimental and analytical interaction ($P\text{-}M$) diagrams were also constructed to investigate the axial and flexural behavior of different groups of specimens.