Flexural strength and deflection characteristics of high-strength concrete beams with hybrid FRP and steel bar reinforcement

The flexural strength and deflection of high-strength concrete beams reinforced with multiple layers of reinforcement and combinations of different reinforcement types (steel, GFRP, and CFRP bars) were evaluated experimentally and analytically. Three beam specimens, reinforced with a single type of reinforcement, and three other specimens, reinforced with a combination of different types of reinforcement, were constructed and tested. An investigation was performed on the influence of hybrid reinforcing with multiple layers of steel or FRP flexural reinforcements on load-carrying capacity, post cracking stiffness, cracking pattern, and ductility. The low post cracking stiffness, high deflection, deep crack propagation, large crack width, and low ductility of FRP bar-reinforced beams were controlled and improved by hybrid reinforcing with steel bars. The test results were compared with the cracking and ultimate moment predictions of ACI Code, and with the service deflection predictions of ACI 440.1R-06 and Bischoff. In addition, alternative service deflection prediction models for hybrid reinforced concrete beams with multiple layers of steel or FRP bars were proposed based on the effective moment of inertia approach of ACI 440.1R-06 and Bischoff.