Corner Strip-Batten Technique for FRP-Confinement of Square RC Columns under Eccentric Loading

In the present study, a new method is introduced for confining square concrete columns in which fiber-reinforced polymer (FRP) strips are used at corners and FRP battens on column sides. In this method, FRP battens confining the section do not undergo any curvature but similar to what happens in flat coupons, they are stretched as completely flat strips. To compare the proposed method with the intermittent wrap technique, 25 square reinforced-concrete (RC) columns with cross-sections of $133\times 133\mathrm{mm}$ and heights of 500 mm were subjected to load eccentricities of 0, 30, 60, 90, and 120 mm. The test parameters included the technique employed for confining columns, flexural strengthening technique, and applied load eccentricity. The experimental results demonstrated that confining battens in the new method of corner strip-batten are uniformly stretched under the tension stresses of confinement; therefore, more-uniform distribution of confining pressure on section occurs and stress concentration at corners is eliminated. Thus, compared to both unconfined and intermittently-wrapped RC columns, square RC columns confined through the corner strip-batten technique exhibit improved performance in terms of enhanced load-carrying capacity and ductility under eccentric loading. Finally, axial loading–bending moment (P–M) interaction diagrams were drawn for the strengthened columns. Comparison of the experimental results with those obtained from the expressions suggested in different codes revealed that the estimates of the codes were conservative when compared to experimental measurements.