Behavior of axially loaded low strength concrete columns reinforced with GFRP bars and spirals

This paper investigates the behavior of circular concrete columns reinforced with glass fiber reinforced polymer (GFRP) bars and spirals under axial load. Nine circular low strength concrete columns of 230 mm diameter and 1500 mm height were constructed and tested. The test parameters included reinforcement type (GFRP and steel), longitudinal reinforcement ratio, and spacing of spirals. Most tested columns showed two peak loads. Test results revealed that the GFRP-RC columns behaved similarly to the steel-RC counterparts. However, the GFRP-RC columns gave a slightly lower first peak load compared to their counterparts reinforced with steel. Increasing the GFRP reinforcement ratio slightly enhanced the capacity of the columns. Highly confined columns showed better ductile failure and significantly increased the second peak load of the columns. Design equations that predict the capacity of FRP-RC columns were evaluated using the experimental data of this study. The results showed that the Canadian Standard Association equation was conservative especially for columns with high reinforcement ratios. In addition, three different confinement models were used to predict the maximum confined concrete strength and they gave reasonable predictions compared to the experimental ones. Furthermore, an existing analytical model was used to predict the load-axial displacement of the tested columns and it showed reasonable correlation with the experimental ones up to the first peak loads. However, significant deviations were observed at the post-peak stages.