Research on the flexural behavior of polypropylene fiber reinforced concrete beams with hybrid reinforcement of GFRP and steel bars

To study the flexural behavior of glass fiber (GFRP) bars and steel bars hybrid reinforced polypropylene fiber concrete (Hybrid-PFRC) beams, one GFRP-PFRC beam, one Steel-PFRC beam, and five Hybrid-PFRC beams were designed and fabricated. The effects of the different area ratio ($${{A_{f} } \mathord{\left/ {\vphantom {{A_{f} } {A_{s} }}} \right. \kern-0pt} {A_{s} }}$$ A f / A s ) of GFRP to steel bars and polypropylene fiber (PP) volume fraction on the flexural behavior of Hybrid-PFRC beams were investigated through experiments. The research results indicated that the Hybrid-PFRC beams’ load–deflection curves exhibited trilinear characteristics with specimen cracking and steel bars yielding as turning points. As $${{A_{f} } \mathord{\left/ {\vphantom {{A_{f} } {A_{s} }}} \right. \kern-0pt} {A_{s} }}$$ A f / A s increased, the flexural bearing capacity of Hybrid-PFRC beams increased, the deflection decreased, the crack spacing and width decreased, and the ductility decreased. The addition of PP did not significantly improve the flexural bearing capacity and cracking moment of Hybrid-PFRC beams, but it greatly enhanced the ductility of the beam. Moreover, PP had good advantages in controlling crack propagation in the beam. The article also used the theoretical model to predict and analyze the flexural behavior of Hybrid-PFRC beams. When predicting the maximum crack width of Hybrid-PFRC beams, when PP is not added to the beam, the bonding coefficient k_b should be greater than 1.4; When PP is added to the beam, it is recommended that the bonding coefficient k_b should not exceed 1.4.