Flexural Behavior Of Concrete Beams Reinforced With Hybrid FRP And HRB Bars

This paper reports and compares experimental studies on flexural performance of concrete beams reinforced with hybrid fiber reinforced polymer(FRP)and steel bars with this study and other literatures are as following.1.Experimental study on mechanical properties and bonding properties of FRP bars are carried out.In this paper,basalt fiber reinforced polymer(BFRP)bars,carbon fiber reinforced polymer(CFRP)bars and glass fiber reinforced polymer(GFRP)bars are selected.Through the tensile test of FRP bars and the bond test of FRP reinforced concrete specimens,the failure modes of tensile test and bonding test of FRP bars and the difference between FRP bars and rebar properties are compared,and the tensile strength,elastic modulus and bond strength of FRP tendons are obtained.The test results show that the ultimate tensile strength of FRP bars is about 1.37-3.29 times of steel bars,but the modulus of elasticity is about 20%-67% of steel bars.The mechanical bite force between FRP bars and concrete can be increased by means of surface sandblasting or rib processing,so it is feasible to use FRP bars in concrete structures for hybrid reinforcement.2.Theoretical research on flexural behavior of concrete beams reinforced with hybrid FRP and steel bars(hereinafter referred to as "hybrid reinforcement").According to the principle of equal strength replacement,two kinds of hybrid reinforcement ratio are defined.According to the principle of "equal strong replacement",two kinds of hybrid reinforcement ratios are defined according to the conversion of strength and elastic modulus.Combined with the design code of concrete structure and foreign related specifications,this paper analyzes the stress stage and failure mode of hybrid reinforced concrete beam.Deducing the calculation formula of crack moment and ultimate moment based on the assumption of plane section and obtaining the calculating theoretical formulae of average crack spacing,crack width and deflection through taking into account the difference of bond properties between FRP bars and steel bars.The related content can provide a reference for the design of hybrid reinforced concrete beam and the formulation of relevant specifications.3.Experimental study on flexural behavior of concrete beams reinforced with hybrid FRP bars and steel bars.Selecting suitable GFRP bars and BFRP bars,8 concrete beams reinforced with FRP bars and steel bars and 3 ordinary reinforced concrete beams have been designed and tested,the crack moment,the ultimate moment,the load-deflection relation,the crack initiation process,crack width and spacing of the hybrid reinforcement concrete beams are compared and analyzed with the reinforced concrete beams.The test results show that,it is feasible to use FRP bars to replace corner bars under equal strong replacement conditions,the bearing capacity of the hybrid reinforced concrete beam is reduced by about 3%~9%.Under the same load level,the deflection of the hybrid reinforced concrete beam is about 1.2~1.94 times of the reinforced concrete beam,and the maximum crack span is about 1~2.63 times.According to the relative test results of domestic and foreign scholars,the correctness of calculation formulas of bearing capacity,crack and deflection of mixed reinforced concrete beams is verified by the comparison between the experimental values and the theoretical calculation values.The relevant test and theoretical analysis results can provide some reference for practical engineering application of mixed reinforced concrete members.4.Experimental study on flexural behavior of hybrid reinforced high strength concrete beams.Four hybrid reinforced concrete beams and two steel reinforced concrete beams were designed and fabricated.The steel fiber reinforced concrete(SFRC,CF50 grade)with high strength was used in the experimental design.Through the flexural test completed,the flexural properties of SFRC beams reinforced with hybrid bars and ordinary concrete(C30)beams reinforced with hybrid bars were compared and analyzed.The test results show that when the load is at 0.7Mu,the strain of the high-strength concrete beams is 1.5-6 times that of the ordinary concrete beams.The cracking moment of concrete beams increases with the increase of concrete strength.Under the same reinforcement ratio,the flexural capacity of concrete beams reinforced with hybrid bras increases with the increase of concrete strength.Reasonable improvement of concrete strength is one of the effective ways to improve the flexural capacity of concrete beams reinforced with hybrid bars.Under normal service condition,the strain along the beam height of the normal section of SFRC beams reinforced with hybrid bars still conforms to the assumption of plane section.Under the same reinforcement form,the flexural capacity of SFRC beams reinforced with hybrid bars increases with the increase of reinforcement area ratio.Under the same conditions,the ultimate moment of SFRC beams with single-layer reinforcement is larger than that with double-layer reinforcement.