Axial Capacity of Circular Concrete Columns Reinforced with GFRP Bars and Spirals

Abstract

Several codes and design guidelines are now available for the design of concrete structures reinforced with fiber-reinforced polymer (FRP) bars under flexural and shear loads. Yet, because of a lack of research, North American codes and design guidelines do not recommend using FRP bars as longitudinal reinforcement in columns to resist compressive stresses. This paper reports on 12 full-scale circular reinforced concrete (RC) columns that were tested under concentric axial loads. The columns were reinforced with longitudinal glass FRP (GFRP) bars and newly developed GFRP spirals. The 300-mm diameter columns were designed according to code requirements. The test parameters included reinforcement type (GFRP versus steel); longitudinal FRP reinforcement ratio; and the volumetric ratios, diameters, and spacing of spiral reinforcement. The test results indicated that the GFRP and steel RC columns behaved in a similar manner. The average load carried by the longitudinal GFRP bars ranged between 5% and 10% of the maximum load. The ductility and confinement efficiency can be better improved by using small GFRP spirals with closer spacing rather than larger diameters with greater spacing. Ignoring the contribution of GFRP bars in the design equation underestimated the maximum capacity of the tested specimens.