Effect of tie spacing and GFRP rebar diameter on compression behavior of concrete columns

Recent research studies have shown encouraging results of using GFRP (glass fiber reinforced polymer) rebars as column reinforcement. However, there are still no guidelines for deciding the tie spacing for different rebar diameters due to limited studies on these aspects. This study explored the influence of some parameters on the compression response of concrete columns having GFRP rebars. The parameters included: (i) 2 bar diameters of GFRP (12 and 8 mm) with almost the same percentage of rebars, (ii) three spacing of ties (6db, 8db, and 12db, db = longi-tudinal rebar diameter), and (iii) eccentricity of applied compressive load (zero eccentricity and eccentrically loaded columns). The performance of these columns was also compared with col-umns reinforced with steel bars. Ten columns (250 x 250 x 1000 mm) were tested up to collapse under eccentric and concentric loadings. The experimental results revealed that there was almost no effect of the change in rebar diameter on column behavior, and the optimal spacing of ties was found to be 8db. An analytical procedure was provided for predicting the load-moment interaction plots of FRP-reinforced columns. The predictions were either reasonably close or a little conservative.