Analysis and prediction of the short‐term flexural stiffness of a steel‐Fiber Reinforced Polymer composite bar‐reinforced concrete beam

Abstract Steel‐fiber‐reinforced plastics composite bars (SFCBs) are a new material that can effectively solve the problems of low stiffness and poor ductility in fiber‐reinforced plastics (FRP)‐reinforced concrete members. To study the flexural performance of SFCB concrete beams, flexural testing of SFCB test beams is carried out in this study, and the flexural stiffness and failure mode of SFCB concrete beams are studied in detail. The results indicate that the failure process of SFCB‐reinforced concrete beams can be divided into three main stages: elastic, cracking, and failure. Due to the presence of external fiber layers, the load‐carrying capacity can continue to increase steadily after the yielding of the steel core, exhibiting stable secondary stiffness and good ductility characteristics. At the same reinforcement ratio, the flexural stiffness of SFCB concrete beams is between that of steel‐reinforced concrete beams and FRP‐reinforced concrete beams. Increasing the steel content of SFCB can effectively improve the flexural stiffness of the test beams, while the influence of concrete strength on flexural stiffness is relatively weak. The existing codes or stiffness calculation models cannot accurately predict the short‐term flexural stiffness of SFCB concrete beams. Based on existing research studies, this paper further determines and proposes a calculation formula for the flexural stiffness of SFCB concrete beams and verifies it with the test results. The results show that the proposed formula is in good agreement with the experimental results.