Bond strength improvement of GFRP rebars with different rib geometries

Based on the Canadian Standards Association (CSA) criteria, 105 pullout specimens were tested to investigate the effect of different rib geometries on bond strength of glass fiber reinforced polymer (GFRP) rebars embedded in concrete. Two kinds of conventional reinforcing rebars were also studied for comparison. Each rebar was embedded in a 150 mm concrete cube, with the embedded length being four times the rebar diameter. The experimental parameters were the rebar type, rebar component, rebar diameter, rebar surface texture, rib height, rib spacing and rib width. Theoretical analysis was also carried out to explain the experimental phenomena and results. The experimental and theoretical results indicated that the bond strength of GFRP rebars was about 13%∼35% lower than that of steel rebars. The bond strength and bond-slip behavior of the specially machined rebars varied with the rebar type, rebar diameter, rebar surface texture, rib height, rib spacing and rib width. Using the results, design recommendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics, which concluded that the optimal rib spacing of ribbed rebars is the same as the rebar diameter, and that the optimal rib height is 6% of the rebar diameter.