عنوان مقاله [English]
Application of Fiber Reinforced Polymers (FRP) composites is one of the most prevalent methods for retrofitting concrete structures. Strengthening of columns as a major member of structures which undergo 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 the both ends of the column. The lateral deflection would lead to secondary moment which its combination with 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 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 increase in slenderness. In other words, the bearing capacity of FRP is not used completely and the column is vulnerable to instability and buckling. As a result of that, slenderness effect may refrain the column to achieve its maximum bearing capacity. In this study, six concrete specimens in height of 900 mm under eccentric loading with 60 mm eccentricity were tested. Half of the specimens were with circular cross section and half with square cross section. All the specimens are retrofitted with FRP composites in longitudinal direction by the means of externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) method. Results show that in column strengthened via EBROG method, load carrying capacity is more than reference and EBR columns. Furthermore, EBROG method decreases secondary effects and increases ductility index in slender columns compare to reference and EBR columns.