Experimental and Theoretical Study on Tensile Mechanical Properties of GFRP–Steel Composite Bars

Glass-fiber-reinforced polymer (GFRP)–steel composite bar, a novel building material, is a promising longitudinal reinforcement for marine engineering in harsh environments. Previous research has primarily focused on altering individual parameters to assess their influence on the performance of composite bars, lacking a systematic and in-depth exploration. In this paper, the tensile properties of composite bars have been investigated by adequate experimental testing considering the type of inner steel bar and the thickness of the GFRP layer. Results show that although composite bars undergo elasticity, hardening, and failure stages under tensile loading, due to differences in interfacial bonding forces, the ultimate failure mode for composite bars with HPB300 inner steel bars is relative slippage, while for those with HRB400 inner steel bars, it is fracturing. While ensuring that composite bars have good initial elastic modulus and durability, it is preferable for the thickness of the external GFRP layer to be as small as possible. However, the thickness of the external GFRP layer of composite bars should not be less than 2 mm to prevent misalignment of the inner steel bars, which can negatively impact the tangent modulus during the hardening stage and the ultimate tensile strength. Furthermore, a stress–strain constitutive model for this composite bar was developed and validated. This model offers a universal framework for accurately representing the mechanical properties of the material across a wide range of research parameters.