Experimental Study On Flexural Reinforced RC Beams With U-jackets

The resin-based fiber reinforced composite material(referred to as "FRP" or "composite material")is externally bonded or near surface mounted reinforced in the tensile part of the reinforced concrete beam to improve its bending capacity.It is one of the mainstream technologies for flexural reinforcement of reinforced concrete structures.Reinforced concrete beams with composite reinforcement are usually damaged by the intermediate crack debonding or the debonding of the concrete cover.The maximum strain of the reinforcement composite is usually only 20%～40% of the ultimate tensile strain,resulting the characteristics of high tensile strength of composite materials are not well played.Reasonable anchoring measures can effectively control or delay the debonding damage,thus improving the reinforcement efficiency and the utilization rate of the composite material.Domestic and foreign scholars have proposed different forms of anchoring measures,and their effects,durability and construction complexity are different.The research group proposed a diagonal U-Jackets for controlling or delaying the plate end debonding damage.In this paper,13 foot-sized beams were set up,and the mechanism of strengthening reinforced concrete beams with U-Jackets confined NSM method CFRP was studied in three batches.The specific research contents include :(1)comparative study on the influence of mechanics mechanism of inclined U-Jackets strengthened beams with EB method and NSM method.(2)explore the influence of the width of the vertical U-Jackets on the mechanical mechanism of the reinforced beams by NSM method.(3)explore the influence of the width of the 45 degree oblique U-Jackets on the mechanical mechanism of the reinforced beam by NSM method.(4)explore the influence of concrete strength on the mechanical properties of reinforced beams by NSM method.Based on the study of the form and width of CFRP U-Jackets,the following conclusions are drawn :(1)under the premise of the same strengthening amount of CFRP in the bottom plate,the performance of the reinforced beam by NSM method is better than that by EB method,and the oblique U-Jackets are more limited to limit the end debonding failure of thereinforced beam by NSM method.(2)under the premise that the number of vertical U-Jackets layers are unchanged,the vertical U-Jackets can increase the ultimate loads,ultimate deflection,ductility index and the utilization rate of CFRP material to a certain extent,and with the increase of its width,the debonding of end concrete tends to transfer to the intermediate crack debonding.(3)on the premise that the number of 45-degree oblique U-Jackets layers remains unchanged,the 45-degree oblique U-Jackets can increase the ultimate loads,ultimate deflection,ductility index and utilization rate of CFRP materials of the beam to a certain extent,and with the increase of its width,the intermediate crack debonding has been observed in the anchored beam with 150 mm width of U-Jackets.(4)under the premise that the strengthening amount of CFRP remains unchanged,higher concrete strength can improve the ultimate loads,ultimate deflection and utilization rate of CFRP materials of beams.(5)on the premise that the width of 150 mm oblique U-Jackets remains unchanged,increasing the number of U-Jackets layers can increase the degree of intermediate crack debonding,increase the ultimate loads,ultimate deflection,ductility index and utilization rate of CFRP material to a certain extent,and achieve better anchorage effect.