Design recommendations for bond between GFRP/steel wire composite rebars and concrete

Due to significant advantages over GFRP rebars, namely high tensile strength, high elastic modulus, and good ductile properties, GFRP/steel wire composite rebars offer a superior alternative to ordinary steel rebars. However, experimental researches on this new type of rebar have been limited, especially those on the bond performance. This research is designed to investigate the bond behavior between GFRP/steel wire composite rebars and concrete. According to American Concrete Institute (ACI) code, a total of 180 pull-out specimens were tested under monotonic static loading conditions. The test parameters were the rebar rib spacing, rebar diameter, embedded length, concrete compressive strength, concrete cover thickness, and concrete cast depth. Based on the numerical analysis of the test results, new criteria for acceptable bond performance of GFRP/steel wire composite rebars to concrete were developed. Designed recommendations for the modification factor of concrete cover thickness, the modification factor of concrete cast depth, and the critical value of bond slip at both free and loaded ends were derived. The calculation formula of bond strength and the basic development length were proposed, and the calculation principle of development length of concrete structures reinforced with GFRP/steel wire composite rebars was suggested.