A Recalibration of the Crack Width Bond-Dependent Coefficient for GFRP-Reinforced Concrete

Serviceability requirements can often control the design of glass fiber-reinforced polymer (GFRP)-reinforced concrete flexural members due to the lower stiffness of GFRP than of steel. ACI Committee 440 crack control provisions for GFRP-reinforced concrete mimic those from ACI 318 for steel-reinforced concrete, but with the addition of a bond-dependent coefficient, kb, to account for differences in bond between GFRP and concrete from steel and concrete. The recommended value for the bond-dependent coefficient in ACI 440.1R-15 is 1.4. This value is largely based on one experimental study, with one type of GFRP bar. Since that study, many more experiments have been performed to examine crack widths in GFRP-reinforced concrete. A database of these experiments that satisfy a rigorous set of criteria to ensure valid experimental results was created from the literature and used to recalibrate the bond-dependent coefficient. A value of 1.2 is recommended for all bars that include a sand coating in the surface enhancement. A value of 1.4 is recommended for all other bars.