Compression behavior of FRP-strengthened RC square columns of varying slenderness ratios under eccentric loading

FRP sheets have been extensively used for the strengthening of reinforced concrete (RC) short columns. However, their application in the strengthening of slender RC columns, especially under eccentric loading, has been very limited. In this paper, the compression response of FRP-strengthened RC square columns of varying slenderness ratios under eccentric loading is studied. The columns were strengthened using both longitudinal and hoop carbon FRP (CFRP) sheets. Three groups of 150 mm square columns of 600, 900, and 1200 mm height were prepared. The RC columns of 600 and 900 mm height belong to the short column category, whereas the column of 1200 mm falls into the category of a slender column. In each group, there were four RC columns. Out of these four columns, one was kept unstrengthened, whereas the other three were strengthened using externally bonded CFRP sheets. The unstrengthened column in each group was considered as a control specimen. The three strengthened columns were prepared by: (i) wrapping one layer of hoop CFRP sheet, (ii) bonding two layers of longitudinal CFRP sheets over the entire surface of the column and wrapping a single layer of hoop CFRP laminate over them, and (iii) bonding four layers of longitudinal CFRP sheets with the other details same as (ii). All the column specimens were tested under compressive load acting at an eccentricity of 25 mm. The test results indicate that the longitudinal CFRP sheets, in the presence of hoop CFRP sheets, control the lateral deflection and substantially improve the load-carrying capacity of the slender columns. The P-M diagrams of FRP-strengthened columns were analytically derived, which were reasonably close to the experimentally observed P-M diagrams.