Experimental Study And Numerical Simulation Of Flexural Behaviors Of High-strength Concrete Beams Reinforced With Hybrid Bars

Fiber Reinforced Polymer(FRP)bars have been considered as an ideal substitute for steel bars in concrete structures due to its corrosion resistance,high strength,light weight and electromagnetic insulation.It can fundamentally solve the problem caused by steel corrosion what is insufficient durability of concrete structure.The failure of concrete members reinforced with FRP bars usually exhibits brittle failure characteristics and its normal use performance is poor,which greatly limits the promotion and application of FRP bars in practical engineering.In order to improve the normal behaviors and flexural behaviors of concrete structures reinforced with FRP bars,many domestic and foreign scholars have carried out many attempts.On the one hand,the form of hybrid reinforced with FRP bars and ordinary steel bars(hereinafter referred to as"hybrid reinforcement")can improve the durability of concrete structures while improving their security and suitability.On the other hand,some scholars start from increasing the concrete strength grade and use high strength concrete to give full play to the high-strength characteristics of FRP bars in the components,such as steel fiber reinforced concrete.However,scholars have relatively little analysis and discussion on the bearing performance and optimization design of hybrid reinforced high-strength concrete structural members,which needs further study.In view of this,this article was supported by the National Natural Science Foundation of China(51578267),FRP bars,ordinary steel bars and steel fiber reinforced concrete were combined in this test,and the flexural behaviors of high-strength concrete beams reinforced with hybrid Glass/Basalt FRP(GFRP/BFRP)bars and ordinary steel bars was studied by the combination of experimental research and numerical simulation.The main contents and results are shown as follows.1.Experimental study on mechanical properties degradation of GFRP/BFRP bars in high-strength concrete under natural environment.The GFRP/BFRP bars were placed in the inner corner of the high-strength concrete beams.After the beam specimen was placed outdoors for 365 days,the concrete was crushed and the specimens of GFRP/BFRP bars were taken out.The law of mechanical properties degradation of GFRP/BFRP bars before and after concrete wrapping were compared and analyzed.The results show that the alkaline environment of concrete has a greater impact on FRP bars.Compared with the laboratory environment,the mechanical properties(the tensile strength,bending strength and shear strength)of the two types of FRP bars in the concrete environment are reduced to varying degrees,but the tensile elastic modulus and flexural elastic modulus do not change much.After the above analysis,and considering the safety of the concrete structure with FRP bars,the reduction coefficients of tensile strength of GFRP and BFRP bars in concrete under natural environment should be taken as 0.7.2.Theoretical study on the flexural behaviors of high-strength concrete beams reinforced with hybrid bars.The proposed calculation formulas for the balance reinforcement ratios,crack moment and ultimate bending moment of hybrid reinforced high-strength concrete beams reinforced with hybrid bars were derived on the basis of considering the tensile strength of concrete(steel fiber high-strength concrete)in the tension zone.And the proposed calculation formulas for average crack spacing,short-term maximum crack width and mid-span deflection were given based on the difference of the bonding properties between GFRP/BFRP bars and ordinary steel bars.Related research can provide a theoretical basis for the design and practical engineering application of concrete members reinforced with hybrid bars incorporated steel fibers.3.Experimental study and comparative analysis of flexural behaviors of high-strength concrete(CF50)beams reinforced with hybrid bars.Taking the hybrid reinforcement ratio and area ratio of bars A_f/A_s as the main parameters,the flexural behaviors of the hybrid reinforced high-strength concrete beams were tested.With the relevant test results in the previous stage of the research group,the influence of concrete strength(CF50,C30)on the flexural behaviors of concrete beams reinforced with hybrid bars were compared and analyzed.The results show that the balanced reinforcement ratio theory can be used to predict the failure mode of hybrid reinforced high-strength concrete beams.Under the premise of ensuring proper reinforcement failure of the test beams,reasonable increase of the ratio of hybrid reinforcement and increase of concrete strength can effectively improve the flexural bearing capacity of the hybrid reinforced concrete beams.And rationally optimize the reinforcement area ratio A_f/A_s of hybrid reinforced high-strength concrete beams to meet the deformation control requirements of the members.The cracking moment,ultimate bending moment,average crack spacing,short-term maximum crack width and mid-span deflection recommended calculation formulas have good applicability.4.Numerical simulation study on the flexural behaviors of high-strength concrete beams reinforced with hybrid bars.Based on the preliminary experimental results and the finite element software ANSYS,the nonlinear finite element models of high-strength concrete beams reinforced with hybrid bars were established.The numerical simulation results and corresponding test results were compared and analyzed.While further verifying the flexural behavior of hybrid reinforced high-strength concrete beams,the feasibility of the numerical simulation study was determined.The results show that the error between the tested values and the measured values of the crack moment of the hybrid reinforced high-strength concrete beams is large,and the tested values of the ultimate bend moment is in good agreement with the measured values.The simulation of the crack moment and ultimate flexural moment is consistent with the measured results.The load-span mid-deflection simulation curves of the hybrid reinforced high-strength concrete beams agree well with the measured curves under normal use.