Experimental Study On The Flexural Behavior Of BFRP Bar-reinforced High-strength Concrete Beams With Steel Fibers

Concrete structure reinforced with fiber reinforced polymer (FRP) bars can usually cause a greater deflection and crack width. In order to get perfect durability and serviceability, a new structural system would be formed by use of steel fiber reinforced high strength concrete and FRP bars. Combining with the experimental researches and theoretical analysis, the flexural behavior of BFRP bar-reinforced high-strength concrete beams with steel fibers were studied in this paper, and the main results are as follows:(1) An investigation was performed for the influence of ratio of reinforcement for FRP bars and fraction of steel fiber by volume on the load-bearing capacity of beams. The appearance and development of cracks, also failure mode was described. While, the changing trend of FRP reinforcement stress, deflection, crack width were analyzed. The test results indicate that steel fiber remarkably improved the working performance of BFRP bar-reinforced high-strength concrete beams with steel fibers.(2) Based on the experimental research in this paper and the recent developments at home and abroad, the difference of the over reinforced beams and insufficient reinforced beams in failure mode as well as mechanical behavior were analyzed. It can be seen that plane sections before bending remain plane after bending. Then, the special calculation model of the BFRP bar-reinforced high-strength concrete beams with steel fibers at different reinforcement ratio and fraction of steel fiber were given, and the calculating methods of the ultimate moment capacities were established using the limit equilibrium theory.(3) Considering the favorable effect of steel fiber on restricting crack width of concrete beams, the value of Kf revealed that the linear trend of over reinforced member and the broken line trend of insufficient reinforced member. Thus, The modified formula of maximum crack width based on the ACI code for the BFRP bar-reinforced concrete beam with steel fibers were put forward.(4) The calculating methods for predicting the deflection of the BFRP bar-reinforced high strength concrete beam were proposed by modifying calculation method of the effective moment of inertia for traditional RC flexural members in ACI code.(5) Based on the brittle failure characteristic of the specimens, the definition, evaluation index and calculating mode of ductility of the BFRP bar-reinforced concrete beam with steel fibers were proposed, and the accuracy was also be verified by the experimental data.