Study On Secondary Mechanical Shear Behavior Of Concrete Beams Strengthened With FRP Rigid Grid-ECM

As the service time of the structure increases,the structural damage accumulates continuously,resulting in the continuous reduction of structural reliability.Therefore,it is urgent to improve the reinforcement technology to improve the bearing capacity of the structure and ensure the normal service time of the structure.Fiber reinforced polymer(FRP)has become a research hotspot of scholars at home and abroad because of its light weight,high strength,simple construction and corrosion resistance.In recent years,scholars at home and abroad have proposed to use FRP rigid grid-epoxy mortar(ECM)to strengthen concrete structures.In this technology,the FRP rigid grid and ECM form a composite reinforcement layer and bond with the original component to form a whole,so as to improve the bearing capacity and stiffness of the component.At present,the research on this technology is still in the initial stage,and the influence of secondary stress and other related factors on the reinforced members is not considered,which deviates from the reinforcement process in the actual project.Therefore,based on the condition of changing the grid size and reinforcement mode under secondary stress,this paper carries out the shear performance test and theoretical analysis of FRP rigid grid-ECM reinforced RC beams.The main research contents of this paper are as follows:(1)Strengthening reinforced concrete beams with FRP rigid grid-ECM can not only increase the stiffness and ductility of the beam,but also effectively delay the development of main inclined cracks,change some crack forms and form stepped cracks.During the stress process of FRP rigid grid,the shear force borne by the vertical fiber strip is much larger than that of the horizontal fiber strip,and the horizontal fiber strip lags behind the vertical fiber strip,but this lag effect will gradually decrease with the amplitude of preload reaching 50%Pu or above.(2)The higher the amplitude of preload,the worse the effect of shear reinforcement.The ultimate bearing capacity of the strengthened reference beam increased by 22.51%compared with the unreinforced beam,and the ultimate bearing capacity of the pre-loaded 80%Pu strengthened beam increased by 10.61%compared with the unreinforced beam.Under the same level load,the higher the amplitude of preload,the smaller the reduction of deflection,reinforcement and FRP rigid grid strain.With the increase of preload amplitude,the FRP rigid grid will enter the working state earlier.When the preload amplitude reaches 50%Pu or above,with the increase of the degree of pre damage,the strain fluctuation amplitude of FRP rigid grid becomes larger and the peeling degree is obvious.(3)For the strengthened beams with three bonding methods,the reinforcement effect of all beams strengthened with FRP rigid grid is better than that of transverse bonding and oblique bonding in bending and shear zone,and the deformation resistance and stiffness of beams strengthened with FRP rigid grid with 45° in bending and shear zone are the second.Compared with beams strengthened with full FRP rigid grid,the way of pasting FRP rigid grid in bending shear zone has a certain influence on the inclination angle of inclined cracks.(4)In this paper,the shear force of FRP rigid grid-ECM strengthened beam is mainly carried out by concrete,stirrup and FRP rigid grid.Based on the truss arch theoretical model and the introduction of pre damage influence coefficient,the shear calculation formula of FRP rigid grid-ECM strengthened RC beam under secondary stress is deduced.The theoretical value is compared with the experimental value,and it is found that the calculated value is quite conservative.