Experimental study and design recommendation on the bond between GFRP/steel wire composite rebars and concrete

The bond behavior between GFRP/steel wire composite rebars and concrete is a key issue to the performance of concrete structures reinforced with GFRP/steel wire composite rebars. Pull-out tests were conducted on 180 specimens according to the method of American Concrete Institute (ACI) code. The test parameters included the rebar rib spacing, rebar diameter, embedded length, compressive strength of concrete, concrete cover thickness, and concrete cast depth. For each specimen, the bond strength, the slip both at the loaded and free ends were measured, and the bond-slip relationship curves were calculated. Based on analysis of the test results, the modification coefficient of concrete cover, the modification coefficient of concrete cast depth, and the critical value of bond slip were obtained. The calculation formula of bond strength and the basic embedded length were proposed, and the calculation principle for the embedded length was suggested. The test results and design recommendations can serve as a theoretical basis for determining the concrete cover thickness, formulating the bond-slip constitutive relationship model of the GFRP/steel wire composite rebars, and establishing the related criterions.