Study On Flexural Performance Of CRB750 Steel Bars Reinforced Concrete Beams And Damaged Beams Retrofitted With Steel Plate

CRB750 is a new type of cold-rolled ribbed steel bar with a yield strength of 750 MPa and an elongation of 22%,which achieved high strength and ductility by adding trace rare earth element in steel smelting process.While improving the safety and reliability of building structures,it can greatly reduce the amount of steel used,thereby reducing pollution and carbon emissions.Therefore,it has considerable application prospects in practical engineering.In order to reveal the load-bearing mechanism of CRB750 RC beams and popularize the application of CRB750 steel bars in the engineering field,the flexural properties of CRB750 steel bars reinforced concrete beams and damaged beams retrofitted with steel plate were studied by full-scale model test theoretical analysis,and finite element method,and the following results were obtained.(1)Four-point bending tests were carried out on six CRB750 RC beams and two HRB400 RC beams,and the failure modes,bending moment-deflection curves and strain characteristics of reinforcement and concrete with different reinforcement ratios were obtained.Compared with HRB400 RC beams,CRB750 RC beams had better advantages in bearing capacity and ductility.However,under the condition of equal strength reinforcement,the deflection and the crack width of CRB750 RC beams was larger,and the high strength of CRB750 steel bars used in low-strength concrete was difficult to be fully utilized.(2)Theoretical analysis of CRB750 RC beams were carried out were performed.The characteristics of moment-deflection curves,cracking load,bearing capacity,deflection and crack width of CRB750 RC beams were proposed.The difference between CRB750 RC beams and ordinary RC beams in bending process was summarized.The crack load was analyzed theoretically and the minimum reinforcement ratio of CRB750 RC beams was obtained.Based on the current Code,the flexural capacity of CRB750 RC beams was calculated theoretically,and the height of the compression zone was analyzed theoretically to get the balanced-reinforced ratio of CRB750 RC beams.Finally,the deflection and maximum crack width of CRB750 RC beams were analyzed theoretically,and it was clear whether the deflection and maximum crack width of CRB750 RC beams in normal use could meet the requirements of specification limits.(3)In order to solve the problems of CRB750 RC beams with large crack width and deflection,and difficult to give full play to the advantages of high strength and ductility,finite element numerical simulation was used to study the influence of concrete strength and prestress on the flexural performance of CRB750 RC beams.The research results showed that increasing the concrete strength could improve the ultimate bearing capacity of CRB750 RC beams,and could better play the advantages of high strength and high elongation of CRB750 steel bars.Prestressing could improve the bending stiffness of CRB750 RC beams,reduce the deflection deformation under normal use.(4)A method for recycle use damaged CRB750 concrete beam was proposed,which was obtained by repair the compression zone of with bonded steel.Bending test on repaired steel reuse beams were carrying out to obtain the failure form,flexural bearing capacity,stiffness and ductility of the reused beam.Compared with test results of CRB750 RC beams,it was found that the bearing capacity of reused beams could reach more than 90%of the bearing capacity of the RC beams,and the advantages of high elongation of CRB750 steel bars could be fully utilized.