Investigation of different parameters affecting the crack width and kb coefficient of GFRP-RC beams

Crack width control is one of the criteria affecting the design of glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) structural components. The provisions available in the CSA S806-12 standard and ACI 440.1R-15 guideline for controlling the crack width of GFRP RC elements account for the bond between the GFRP reinforcement and surrounding concrete through the bond-dependent coefficient (kb). In those design standards and guidelines, each GFRP bar surface profile is assigned a kb value obtained from four-point bending beam tests. This study aims to experimentally investigate the parameters that affect the crack width and kb coefficient of GFRP reinforcing bars, enrich the literature with more kb results for ribbed and sand-coated GFRP bars, determine whether kb is a fixed value that is solely dependent on the bar surface profile (as assumed by the above standard and guideline), recalibrate the kb coefficient considering the experimental results of this study and available experimental data in the literature, and provide the FRP engineering community with an equation that is capable of anticipating kb values based on different configurational and material parameters. To achieve the objectives of this study, 16 large-scale RC beams were tested under a four-point bending test setup. The studied parameters included the clear concrete cover, bar spacing, bar diameter, concrete compressive strength, bar surface profile, and confinement provided by transverse reinforcement. The experimental results of this study were combined with the available database to recalibrate the kb values and propose a kb equation. The results showed that the kb coefficient varies when changing the reinforcement configuration of the beam.