231 / 2022-06-13 22:58:48

Flexural behavior and design methods of concrete beams reinforced with a combination of FRP and steel bars

Concrete beam; Flexural behavior; Hybrid reinforcements; Fiber-reinforced polymer bars; Failure mode; Design methods

Concrete beams reinforced with a combination of FRP and steel bars are considered to provide improved serviceability and ductility compared with only FRP bars reinforced concrete beams, superior durability and strength to those of steel bars reinforced concrete beams. This study aims to investigate the effect of reinforcement ratio on the flexural behavior of concrete beams reinforced with a combination of FRP and steel bars. Based on the rectangular stress block hypothesis for the stress distribution in the compressive zone of concrete, the equilibrium of internal forces and strain compatibility, the failure modes of concrete beams with FRP and steel bars were distinguished and the corresponding reinforcement ratio requirements were determined. Seven beam specimens, which were designed to fail in different modes, were constructed and then tested under two loading points. The test results showed all beam specimens failed by FRP rupturing, indicating that the tensile strength of FRP bars were fully used. One beam specimen was over-reinforced, but it failed by FRP rupturing. The reinforcement ratio requirements failed to predict the failure mode and necessitated a reconsideration. The concrete beams with FRP and steel bars exhibited post-yielding stiffness, which was contributed by FRP bars and its magnitude grew with the increase in FRP reinforcement ratio. With the increase in the reinforcement ratio, the flexural capacity and stiffness of concrete beams with FRP and steel bars increased, but the ductility showed an opposite trend. Furthermore, existing design methods were proved to be effective to predict the cracking load, flexural strength and deflection of all beam specimens.