Experimental Study And Theoretical Analysis Of The Mechanical Behavior Of GFRP-steel Hybrid Reinforced Concrete Beams

Fiber reinforced composite bars(FRP bars)have the advantages of high tensile strength,light weight,corrosion resistance,etc.,which can better solve the problem of steel corrosion in reinforced concrete structure,and play an important role in improving the durability of the structure.Since the stress-strain relationship of FRP bars is linear elastic,and the elastic modulus of FRP bars is small,the deflection and crack width of FRP reinforced concrete beams are larger than that of reinforced concrete beams,which affects its wide application in engineering examples.GFRP bars are used to replace some of the bars in the reinforced concrete beams to form GFRP-reinforced concrete beams with hybrid reinforcement,which can better solve the above two problems.In this paper,the flexural behavior of GFRP-reinforced hybrid reinforced concrete beams is theoretically analyzed and experimentally studied.Ten concrete beams are designed,among which 8 are GFRP-reinforced hybrid reinforced concrete beams(including 3 super-reinforced beams and 5 normal reinforced beams),1 reinforced concrete beam and 1 GFRP reinforced concrete beam.The main contents of this paper are as follows:(1)Three failure modes of hybrid reinforced beams: less-reinforced beams,superreinforced beams and normal reinforced beams.The failure characteristics,crack load,ultimate bearing capacity,crack development and deflection of the three types of failure are summarized and analyzed.At the same time,the load-deflection curve,load-reinforcement strain curve,load-gfrp bar strain curve and so on of the beam are given.(2)The boundary conditions of the three failure modes of hybrid reinforced beams,i.e.the failure of few reinforcement,the failure of normal reinforced bar and the failure of super-reinforced bar,are analyzed,and the reinforcement ratio under the conditions of "equal strength" and "equal elastic modulus" are given.The calculation methods of crack width,average crack spacing and deflection of GFRP-reinforced hybrid reinforced concrete beams are summarized.The calculation method of ultimate bearing capacity,bending stiffness of hybrid reinforced beams under short-term load,and the corresponding calculation method of crack width and average crack spacing of GFRP-reinforced hybrid reinforced concrete beams are proposed.When the equivalent nominal reinforcement ratio remains unchanged,increasing the proportion of FRP reinforcement can significantly improve the ultimate bearing capacity.When the ratio of FRP reinforcement remains unchanged,the increase of ultimate bearing capacity is very small,indicating that FRP reinforcement has a great effect on the improvement of ultimate bearing capacity.(3)In this paper,the traditional ductility index,energy ductility index and J index are improved to study the ductility of GFRP-reinforced concrete beams with hybrid reinforcement.The advantages and disadvantages of the three ductility indexes are analyzed and compared,and J index is suggested to be adopted.This index is greater than or equal to 4 and 6 respectively in the rectangular beam and T-shaped beam J index.As the proportion of FRP bars in the total reinforcement ratio increases,the J ductility index becomes smaller and closer to 4.