Bond coefficient, k_b, of GFRP bars

Due to the increase in the number of manufacturers of GFRP bars, there is currently a variety of products in the marketplace with different physical and mechanical properties. These differences directly influence the bond coefficient, k_b, a coefficient intended to relate the behavior of GFRP to that of steel bars for the computation of crack width and deflection of reinforced concrete elements. The 2015 version of the Guide for Design and Construction of Structural Concrete Reinforced with Fiber Reinforced Polymers by ACI Committee 440 recommends a k_b value of 1.4 for bars that have not been experimentally tested. To establish a specific k_b, bars could be experimentally tested according to the 2012 edition of Canadian Standard S806-12. This test method is rather complex and has produced k_b values varying from 0.69 to 1.61 according to published literature. The study presented in this paper determined k_b according to the Canadian test method and a simpler proposed variation. This comparison is based on data derived from twenty-three beams tested to determine k_b for two types of GFRP bars (Type-A and Type-B) and a conventional steel bar (Type-S). Bar Type-A is sand-coated with a helical wrap surface treatment, while Type-B is helically grooved. The investigation yielded similar results for both test methods and indicated some advantages with the use of the proposed test method. The k_b of the Type-A presented a slightly better (lower) k_b than the Type-B.