Tensile Properties of CFRP–GFRP Hybrid Reinforcing Bars and Their Effects on the Structural Behavior of Concrete Members

The relatively low elastic modulus of glass fiber-reinforced polymer (GFRP) bars limits their use in stiffness-sensitive concrete members. This study fabricated hybrid bars by integrating carbon fiber-reinforced polymer (CFRP) at the GFRP surface and experimentally verified the resulting increase in tensile elastic modulus. Four nominal carbon-content groups (0, 4.3, 8.7, and 13.0%) of 10 mm bars were tested, with five specimens per group. Mean modulus increased from 47.79 to 65.54 GPa, corresponding to a maximum gain of 37.1%. Hybrid-bar failure involved separation at the GFRP–CFRP interface. The modulus improvement was accompanied by changes in tensile strength and rupture strain; the H13 mean tensile strength was 12.8% below that of the GFRP control. Finite element analyses extended the investigation beyond the bar tests: measured 10 mm bar properties were used in beam, column, and slab models, while an idealized 19 mm core–shell beam series examined an untested larger-bar configuration. The simulations predicted configuration-dependent changes in load–displacement response and tensile-damage distribution, with small peak-load changes in the 10 mm column and slab models. The primary contribution is the experimentally verified stiffness enhancement achieved through actual surface hybridization; the member analyses identify its potential structural implications. Structural tests and bond characterization remain necessary to validate these predictions and quantify serviceability benefits.