AbstractTen large-scale high-strength concrete (HSC) circular columns were constructed and tested to failure. Nine columns were internally reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals, whereas one was reinforced with steel bars and spirals to serve as a reference. All columns had a diameter of 350 mm. The variables tested were reinforcement type, spiral pitch, slenderness ratio, eccentricity-to-diameter ratio (e/D), and type of loading (axial or four-point bending). Experimental results showed that both reinforcement types (steel or GFRP) and the spiral pitch did not have a significant effect on the behavior of GFRP-reinforced HSC columns up to the peak load. In addition, a decrease in the axial capacity of the columns as the e/D ratio increased was observed. This was consistent for specimens of both slenderness ratios of 14 and 20. Columns with a higher slenderness ratio showed a lower axial capacity for all specimens tested under the same e/D ratio. Furthermore, slender columns with higher e/D ratio underwent much larger deformations; both axially and laterally. For columns of both slenderness ratios, axial load–bending moment interaction diagrams were produced using the experimental results and were compared to the predictions of available codes and guidelines.