Glass　fiber-reinforced　polymer　(GFRP)　reinforcement　has　been　considered　as　a　replacement　for　the　traditional　steel　reinforcement,　mainly　due　to　its　corrosion　resistance.　In　this　paper,　a　total　of　13　concrete　columns　and　beams　(length/diameter　=　5.3)　fully　reinforced　with　GFRP　longitudinal　bars　and　spirals　were　experimentally　studied.　An　additional　two　reference　columns　were　also　constructed　with　steel　rebars　and　GFRP　spirals　to　quantify　the　effect　of　the　long　bars.　Factors　such　as　the　number　of　longitudinal　bars,　the　pitch　of　the　spirals,　and　load　eccentricities　were　examined.　It　was　found　that　the　load　capacities　of　the　specimens　with　GFRP　reinforcement　were　up　to　12.3%　lower　than　those　with　steel　reinforcement;　however,　with　sufficient　transverse　reinforcement,　the　GFRP-reinforced　specimens　were　up　to　15%　more　ductile.　Reducing　the　pitch　of　the　GFRP　spirals　and　increasing　the　number　of　longitudinal　reinforcing　bars　both　resulted　in　an　increase　in　the　ductility　and　load　capacity,　demonstrating　the　contribution　of　transverse　and　longitudinal　reinforcement.　Strains　well　beyond　the　ultimate　strain　capacity　of　the　concrete　were　measured　in　the　longitudinal　GFRP　bars,　illustrating　the　significant　confinement　provided　by　the　spirals.　The　experimental　results　were　favorably　underpredicted　by　the　recommended　simplified　method　derived　in　this　paper.　In　order　to　simplify　the　design　process　of　circular　members,　a　factor　βc　was　introduced　to　the　current　design　rules　in　the　international　design　standards　and　validated　by　the　experimental　results.　©　2020　American　Society　of　Civil　Engineers.