Flexural Behavior Of U-shape FRP Profile-concrete Beams With Confinement At Compression Zone

The problems of reinforced concrete,such as self-weight,poor ductility,poor corrosion resistance and poor durability,not only seriously restrict the use and development of concrete structures,but also affect the seismic performance of structures.In recent decades,FRP has been widely used in the reinforcement of existing concrete structures and the design of various new composite structures because of its excellent performance.Among them,FRP-concrete composite structure system is a hot research direction in recent years.It is usually composed of prefabricated FRP and cast-in-place concrete,which has excellent mechanical behaviour and good application prospects.The failure of reinforced beam members mainly depends on the concrete in the compression zone.The problem of brittle failure of traditional reinforced concrete beams can be solved by local restraint.Restraining the concrete in the compression zone can improve the overall compressive strength and ultimate strain of the compression zone,then the mechanical performance of the beams and seismic capacity of the structure can be also improved.The development of recycled concrete is one of the important ways to solve the problem of increasing construction waste and natural resource shortage.The results show that the mechanical properties of recycled concrete members restrained by stirrups or FRP can be greatly improved.At present,most of the research on restrained recycled concrete structural members mostly biased in column members.In order to promote mass application of recycled concrete,the research on restrained recycled concrete beams needs to be further carried out.Based on the above background,an innovative FRP and concrete composite member with local constraints is proposed in this paper,and recycled concrete beam specimens are also introduced.The flexural behavior of U-shape FRP profile-concrete beams with confinement at compression zone was studied experimentally and theoretically.A total of 14 medium-sized(i.e.1800 mm long,100 mm wide and 160 mm high)beam specimens were constructed and tested under two-point bending,including one ordinary concrete contrast beam(i.e.CB),one recycled concrete contrast beam(i.e.RCB),four FRP concrete composite beams without spiral stirrups confinement at compression zone(includes one FRP-recycled concrete composite beams)and eight FRP concrete composite beams with spiral stirrups reinforcement at compression zone(includes two FRP-recycled concrete composite beams).The examined experimental variables included:(1)different arrangement of C/GFRP layers in U-shape profile,(2)inner spiral stirrups at compression zone and(3)concrete types.Based on the testing,the failure mode,load-deflection relationship,ductility,energy absorption capacity and load-strain relationship of the beams were analyzed.The results indicated that for both ordinary concrete specimens and recycled concrete specimens,U-shape FRP profile helped improve the yield load and ultimate load of all the beam specimens,the use of spiral stirrups at compression zone had a slight increase in the ultimate load of the FRP-concrete beams but resulted in pronounced enhancement of their ductility.Smaller spacing of spiral stirrups had more effect on improving the ductility and deformation capacity of FRP-concrete beams,and it also affected the failure modes.There was little difference in the shape of load-displacement curves of FRP-concrete beam specimens and FRP-recycled concrete beam specimens while the former performed better at bearing capacity and ductility than the latter.The finite element model and non-linear analysis of U-shaped FRP profile-concrete beams with confinement at compression zone were also carried out by using OpenSEES finite element software.The theoretical analysis results were compared with the experimental results,which verified the accuracy and reliability of the finite element simulation,and further verified the correctness of the experimental conclusions.