Research On Load-bearing Mechanism And Shear Capacity Prediction Of BFRP Reinforced Concrete Beams

Since the advent of reinforced concrete structures,the durability of concrete structures caused by corrosion of reinforced steel has always been a major issue in the field of civil engineering.Fiber bars have the advantages of light weight,high tensile strength,good corrosion resistance,and non-magnetic insulation.They can be used as reinforcement materials in concrete structures in harsh environments to replace steel bars,fundamentally solving a series of durability caused by steel bar corrosion Problem,so it has been promoted and applied worldwide.Basalt fiber reinforcement(hereinafter referred to as BFRP)is a new type of fiber reinforcement that appears after glass fiber reinforcement(GFRP)and carbon fiber reinforcement(CFRP),and its performance is somewhere in between.China has independent intellectual property rights in the field of BFRP reinforced composite materials and has internationally advanced production technology,so BFRP bars have broad application prospects in China.In order to promote the application of BFRP bars in the field of concrete engineering,it is necessary to investigate the mechanical properties of BFRP bars in concrete.In view of the above background,this thesis conducted a systematic and in-depth discussion on the shear performance of BFRP reinforced concrete beams(hereinafter referred to as BFRP reinforced beams)through experimental research.Based on the preliminary research of the research group,this thesis expands the experimental scheme,taking the longitudinal modulus of elasticity,the reinforcement ratio,the shear span ratio,and the stirrup reinforcement ratio as variables.Through three-point loading test,the shear performance of the BFRP beam research.Through in-depth investigation of experimental results such as failure mode,bearing capacity,bearing mechanism,specimen stiffness,cracking load,progress of main oblique crack opening,combined with previous research results,we strive to reveal the shear bearing mechanism of BFRP tendon beam,The above attempt to propose a more accurate and feasible quantitative evaluation method of BFRP tendon beam shear capacity.Within the scope of this study,the following useful conclusions were drawn:1.Failure mode and bearing capacityThe increase in longitudinal stiffness relative to the axial stiffness(pl×El)increases the height of concrete in the shear compression zone,constrains the progress of the main diagonal crack opening,and strengthens the truss mechanism,which ultimately leads to an increase in shear capacity.The nominal strength of BFRP stirrups(common steel bars:pv×fy;BFRP bars:pv×(0.4fpru)affects the failure mode and shear capacity of the specimen.As the nominal strength of the BFRP stirrups increases,the failure mode of the test specimens migrates from diagonal tensile failure(stirrup bending failure)to shear compression failure(concrete crushing in the shear compression zone).In this migration process,the shear bearing capacity continues to increase with the increase of the nominal strength of the stirrup,but when the failure mode enters the shear failure,the influence of the nominal strength of the stirrup on the shear bearing capacity decreases,and the shear bearing capacity rises weakly.2.Bearing mechanismThe shear load-bearing mechanism of BFRP tendon beams is similar to that of ordinary RC beams.The external shear force is shared by the "arch mechanism" formed by the longitudinal reinforcement and the concrete in the shear zone and the "truss mechanism" involving the stirrups,but both load-bearing mechanisms It is affected by the relative axial stiffness of the longitudinal reinforcement and the nominal strength of the stirrup.When the longitudinal stiffness of the longitudinal bars is increased,not only the"arch mechanism" is strengthened,but also the more inclined stirrups intersect due to the decrease in the inclination angle of the main diagonal cracks,which enhances the"truss mechanism".The main reason for the increase in bearing capacity;the increase in the nominal strength of the stirrups strengthens the "truss mechanism",and the impact on the "arch mechanism" is not clear.3.Quantitative evaluation of shear capacityThrough the analysis of the experimental results,an evaluation formula for the shear bearing capacity of FRP tendon beams modified based on the domestic JTG 33622018 formula is proposed.Through the verification of a large number of test data at home and abroad,and the comparative analysis with the evaluation results of formulas in various countries,the advantages of the revised evaluation formula in terms of accuracy,safety,rationality,and applicability are confirmed.