EXPERIMENTAL STUDY OF SLENDERNESS EFFECTS ON BEHAVIOR OF CIRCULAR AND SQUARE RC COLUMN STRENGTHENED WITH FRP SHEETS BY GROOVING METHOD UNDER ECCENTRIC

The application of FRP composites is one of the most prevalent methods for retrofitting concrete structures. Strengthening of columns as a major member of structures undergoing concentric or eccentric loads is of considerable importance. The column under eccentric loading experiences lateral deflection at any particular column height, which is defined as an eccentricity for the axial load at both ends of the column. The lateral deflection would lead to the secondary moment, whose combination with the primary moment will produce more significant effects. Although concrete columns are mostly under eccentric loading in practical use and are vulnerable to instability caused by the slenderness effect, limited experimental studies have been conducted on the behavior of slender concrete columns strengthened with FRP composites in comparison with strengthened short columns. Previous studies state that the strength of columns increases with retrofitting with FRP; however, the strengthening effect of FRP on the column under axial-bending (P-M) loading would be reduced with an increase in slenderness. In other words, the capacity of FRP is not achieved completely since the column is vulnerable to instability and buckling. As a result of that, the slenderness effect may prevent the column to achieve its maximum load-carrying capacity. In this study, six concrete specimens in the height of 900 mm under eccentric loading with 60 mm eccentricity were tested. Half of the specimens were with a circular cross-section and half with a square cross-section. All the specimens are retrofitted with FRP composites in the longitudinal direction using externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) method. Results show that for the columns strengthened via the EBROG method, the load-carrying capacity is more than that of reference and EBR columns. Furthermore, the EBROG method decreases secondary effects and increases ductility in slender columns compared with reference and EBR columns.