Study On The Flexural Performance Of Reinforced Concrete Beams Under Secondary Stress With Carbon Fiber Net

Reinforced concrete beams are widely used in the main structures of domestic civil buildings and small and medium-sized bridges.Due to the increase in traffic volume and traffic accidents such as collisions,rollovers,and lateral overturns caused by vehicles overspeeding and overloading,many bridges in operation are seriously damaged,which has exceeded the basic requirements for bridge safety in the current design specifications.Carbon fiber mesh-polymer mortar composite.reinforcement material has the advantages of light weight,high strength,fire resistance and corrosion resistance,and convenient construction,It is widely used in the reinforcement of damaged concrete structures.At present,most of the reinforcement test methods for flexural members only carry out one-time loading and unloading for the reinforced members,and ignore the impact of related factors such as the secondary stress of the structure required by the code,which is different from the actual reinforcement process.Therefore,this paper carried out relevant experimental research,theoretical derivation and numerical simulation for the flexural performance of the carbon fiber mesh reinforced beam under the influence of the secondary force.The main research results were as follows:(1)This paper adopted the carbon fiber mesh-polymer mortar composite reinforcement method,the bending performance of 7 concrete reinforced beams under different preload amplitudes and different reinforcement methods was studied.The test results show that the improvement of the beam’s flexural performance by the carbon fiber mesh-polymer mortar reinforcement system was mainly reflected in the retardation of the beam stiffness degradation process after the steel bar yields.Compared with the unreinforced reference beam,it effectively reduces the strain of the reinforced beam concrete and steel bar.Under the influence of the secondary force,the greater the preload amplitude,the more obvious the hysteresis strain of the carbon fiber mesh,the yield load and flexural ultimate bearing capacity of the reinforced beam will decrease,and the deflection and crack development will also increase.Comparing the test beams with different reinforcement methods under the same preload amplitude,the reinforcement effect of the oblique U-shaped hoop is better,and the rigidity and bearing capacity are significantly improved.(2)Starting from the concrete constitutive model of the compression zone,the carbon fiber reinforced beam under different failure modes was deduced.The ultimate flexural bearing capacity formula,and the calculation criteria for identifying the failure mode of the strengthened beam were proposed.The interpolation fitting method was used to process the derived,the load-neutral axis height equations and applied to the calculation of the short-term stiffness of the strengthened beams at different stages,so as to realize the control and check calculation of the deflection of the strengthened beams under different load levels,avoiding the solution error caused by the parameter value problem.(3)The non-linear full-process simulation of 7 test beams under secondary stress was carried out by using the separate modeling method considering the bond-slip,and the flexural bearing capacity,stress deformation and crack development process of the beams were compared and analyzed.Considering geometric parameters such as U-shaped hoop spacing,number,width and other geometric parameters,the position of U-shaped hoop reinforcement was optimized and analyzed,and a set of optimal solutions was obtained,which has certain guiding significance for carbon fiber mesh reinforced beams in actual engineering.