Fiber-reinforced polymer (FRP) bars offer several advantages over steel bars, including higher tensile strength, lighter weight, and non-corrosiveness. There is currently an increased use of FRP-reinforced concrete structures worldwide. However, due to the low compressive strength and modulus of FRP bars, current FRP design codes such as ACI 440.1R-15 and CSA S806-12, neglect the contribution of FRP bars to the ultimate compressive capacities of reinforced concrete columns. This study aims at investigating the feasibility of using glass FRP (GFRP) bars as internal reinforcement in concrete columns, subject to concentric and eccentric loading. A total of four 180 mm x 180 mm square RC columns with heights of 1000 mm and 1100 mm were tested, including two GFRP-RC columns and two steel-RC columns. One GFRP-RC column was tested under concentric loading, and the other was tested under eccentric loading at an eccentricity-to-width ratio of 44.4%. The two steel-RC columns were replicates of the two GFRP-RC columns, and served as control specimens. All columns were cast with normal strength concrete of 34 MPa compressive strength and had the same longitudinal reinforcement ratio of 2.48%. Steel ties of 10 mm diameter spaced at 180 mm were used as transverse reinforcements in all columns. The results showed that GFRP-RC columns had lower load-carrying capacities than their steel-RC counterparts under both concentric and eccentric loadings. The ultimate capacities of GFRP-RC columns were 22% and 34% lower than their steel-RC counterparts at concentric and eccentric loadings, respectively. Also, the GFRP- and steel-RC columns exhibited similar modes of failure, which were mainly compression-controlled with concrete cover spalling and concrete crushing, under the different loading conditions. No rupture or buckling of longitudinal bars was observed. The contribution of GFRP bars to the ultimate column capacity under concentric loading, was found to be around 10.5%. Therefore, this study recommends that the contribution of GFRP bars to the ultimate capacities of RC columns should not be ignored.