Effect of Bar Surface Geometry on Bond Behavior in GFRP-Reinforced Concrete Beams: Experiments and Design Implications

The significant influence of the geometric properties of the rebar surface on the bond behavior of fiber-reinforced polymer (FRP)-reinforced concrete (RC) members is not adequately covered in current design provisions. Twenty-four hinged-type glass FRP (GFRP)-RC specimens have been tested in the present study to investigate the effect of concrete strength, embedment length, confinement conditions, and surface geometric properties of GFRP rebars on the flexural bond behavior of the specimens. It has been observed that the bond strength between the GFRP rebars and the concrete can be increased (up to 15%) by altering the surface geometric properties of the GFRP rebars. The effect of surface geometry is more pronounced in higher-strength confined concrete specimens with an embedment length of GFRP rebars equal to five times the diameter (d) of the rebar as compared to the other tested specimens. Confinement reinforcement has also been observed to increase the bond strength of the tested specimens by 10%–18%. Furthermore, the effect of the test variables on the mode of failure and the postpeak behavior of the specimens under flexural loading has also been investigated in this study. The findings of the present study strongly demonstrate the necessity of a contribution factor that considers the surface characteristics of GFRP rebars in the estimation of the bond strengths of GFRP-RC members. An equation for bond strength estimation, which considers contributions from bar surface geometry, has also been proposed from the findings of this study. It is imperative that similar factors are incorporated into future versions of design provisions in order to integrate the contributions of bar surface geometries to the bond strength of GFRP-RC members.