Behavior of NSM CFRP reinforced concrete columns: Experimental and analytical work

This paper presents the results of experimental testing on fifteen reinforced concrete (RC) columns repaired or strengthened using Near Surface Mounted-Carbon Fiber Reinforced Polymer (NSM-CFRP) under concentric load, eccentric load with 125 mm eccentricity (balanced state), and pure bending moment load , while considering the effect of several configurations on the interaction diagram. Furthermore, this paper investigates the efficiency of these new configurations in the capacity of the RC columns by varying the direction of CFRP strips to be used as reinforcement. The specimens of RC columns, having cross-sectional dimensions 1200 mm × 200 mm × 200 mm (length × width × height) with 150 mm corbel at both ends (in the plane of bending moment) and 1.13 % steel reinforcement ratio, were used. The specimens were divided into five groups: control group, preloaded until 80 % transversely strengthened group, preloaded until 80 % longitudinally strengthened group, preloaded until 80 % transversely and longitudinally strengthened group, and un-loaded transversely and longitudinally strengthened group. Each group included three specimens with a different type of loading as described above. The overall response of the specimens was investigated in terms of axial load carrying capacity, axial displacement , toughness, and failure modes. Furthermore, the interaction diagram for each group was developed and investigated. The strengthened and retrofitted specimens showed a significant increase in axial capacity and significant enhancement in the interaction diagram for all groups. The study showed that the most improvement in the interaction diagram, for both tension and compression control region, occurred when specimens were strengthened in both directions (transversely and longitudinally). In addition, the interaction diagrams were modified to provide a direct solution for the NSM-CFRP ratio. The modified design model was found to be capable of predicting the axial load capacity of NSM-CFRP strips columns.