Axial and flexural behavior of reinforced concrete columns retrofitted with FRP composites through corner strip-wrap technique

Column strengthening is critically important as one of the fundamental elements in structures. The objective of this study is to investigate the behavior of reinforced concrete (RC) columns strengthened with fiber reinforced polymer (FRP) composites using the novel corner strip-wrap technique when subjected to axial loading with varying levels of eccentricity. In order to compare the proposed method with the wrapping technique, ten square reinforced concrete (RC) columns, each with cross-sectional dimensions of 133×133 mm and a heights of 500 mm, were subjected to zero, 30, 60, and 90 mm load eccentricities. Among these specimens, two columns were confined using the wrapping method, and four columns were confined using the corner strip-wrap technique, while the remaining columns were designated as control specimens. In other words, the test parameters consisted of the technique used for column confinement, and the applied load eccentricity. The experimental results revealed that, in comparison to both unconfined and wrapped RC columns, improved performance in terms of increased ductility and load carrying capacity under eccentric loading was demonstrated by square RC columns when confined through the corner strip-batten technique. Moreover, it is evident that eccentric loads, in contrast of concentric ones, significantly reduce the load carrying capacity and ductility of confined RC columns. However, in this experiment, confined columns exhibited a higher load carrying capacity and greater ductility in comparison to their unconfined counterparts, both in concentric and eccentric testing conditions. For instance, the load carrying capacities of columns confined using the corner strip-wrap technique increased by 15% and 13% when compared to those confined through the conventional wrapping technique when subjected to eccentricities of zero and 90 mm, respectively. Additionally, columns confined with the corner strip-wrap technique demonstrated ductility enhancements of 607% and 330% in comparison to the unconfined columns when subjected to zero and 60 mm eccentricities, respectively. Finally, axial loading-bending moment (P-M) interaction diagrams were created for both the unconfined and confined columns. A comparison of the experimental results with the values derived from the expressions recommended in various codes showed that the code-based estimates were conservative in relation to the experimental measurements.