Abstract: This paper presents the test results of the experimental study on 30 different rib geometries of the glass
fiber reinforced composite(GFRP) ribbed rebars. 90 standard pull-out specimens were used to study the bond behavior of GFRP ribbed rebars to concrete. The test variables were the rebar diameter, the rib spacing and the rib height. For each rebar, the bond strength and the slip at the loaded end were obtained, and the corresponding bond-slip relationship curves were analyzed. Using the optimum criterion, design recommendations were made concerning optimum rib geometries of GFRP ribbed rebars with superior bond-slip characteristics. The test results show that the bond behavior between GFRP ribbed rebars and concrete varies obviously with the rib geometries: the optimal rib spacing of GFRP ribbed rebars is 1 times the rebar diameter, the optimal rib height is 6 % of the rebar diameter, and the optimal ratio of rib height to rib spacing is 0.06.