Slender Columns Reinforced by High-Strength Steel Reinforcing Bars and Retrofitted by Fiber-Reinforced Polymer Sheets

Consumption of high-strength steel (HSS) reinforcing bars is nowadays rising in concrete structures to compensate the deficient strength and corrosion resistance of normal-strength steel (NSS) ones. Where this provision fails to meet ultimate requirements, such concrete members as slender columns might need to be additionally retrofitted with fiber-reinforced polymer composites. In this study, the behavior of nine circular slender columns reinforced with HSS reinforcing bars and strengthened with carbon FRP composites was studied under constant eccentric loading. For this purpose, columns with slenderness ratios in the range of 15.4 to 28 were strengthened using either methods of externally bonded reinforcement (EBR) or externally bonded reinforcement on grooves (EBROG). Results revealed the superiority of the EBROG-strengthened columns over the EBR-strengthened and non-strengthened ones in terms of increased load-carrying capacity and ductility as well as reduced secondary moments for each slenderness ratio tested. Moreover; the EBROG-strengthened columns were found to be less affected by secondary effects than were the ERR ones as slenderness ratio increased (this is evidenced by an increase of 5.9% in secondary to primary moment recorded for the EBROG ones versus the 20% increase for the EBR ones); also, ductility remained unchanged in both the control and EBROG specimens while it decreased by approximately 16% in the EBR ones as a result of increasing slenderness ratio. Finalty, the results and overall behavior of slender column specimens rein forred with HSS rein forcing bars were compared with similar slender columns reinforced with NSS rein forcing bars in terms of strength, secondary effects, and ductility index.