A total of 15 concrete columns were cast and tested to investigate the influence of replacing longitidunal and/or tie steel bars by an equal volume of amount of glass fiber reinforced polymers (GFRP) bars on the behavior of concrete columns. The columns were subjected to concentric monotonic axial loading. The concrete block for all columns was 459X250X1200 mm. The results indicated that replacing the longitudinal steel bars by GPRP bars reduced the axial capacity of the column by 13%. The results also showed that regardless of the type of the longitudinal bars, replacing the steel ties by GFRP ties reduced the axial capacity of the column by 10%. However, the study revealed that replacing the steel ties by GFRP had, up to about 80% of the ultimate load, no influence on the load axial shortening curve. Furthermore, the results indicated that the currently used ACT formula to estimate the axial capacity of the column overestimated the actual capacity of the column reinforced longitudinally and or transversely by GFRP bars.