Experimental Study On Flexural Behavior Of RC Beams Strengthened With CFRP Sheet Under Quadratic Loading

At present,concrete structure is one of the main structure forms of buildings.Due to the corrosion of steel,concrete carbonization,earthquake action,environmental impact and accidental factors,the flexural capacity of the structure is insufficient,so it is necessary to strengthen the structure effectively.Fiber reinforced composite(FRP) is a new type of material widely used in structure strengthening.It is light(about 1/5 steel) high strength(some higher than 3000MPa),good corrosion resistance,designability.It is light(about 1/5 steel)high strength(some higher than 3000MPa),good corrosion resistance,designability.The advantages of rapid construction and selfweight and volume increase after strengthening have been widely recognized and applied by academic and engineering field at home and abroad.At present,most of the research on fiber reinforced composites(FRP) reinforcement methods are directed to a single loading beam,but in actual engineering,the building structure tends to have different loading states before reinforcement,which leads to a problem of quadratic loading.In this paper,the flexural performance test of seven concrete beams were carried out by using the CFRP strengthening method.The flexural performance of the strengthened beams under different preload values,reinforcement layers and loading history was studied.Different parameters were analyzed.The effect on the strengthening effect of CFRP.The research results show that the CFRP strengthening method can effectively improve the ultimate flexural capacity of the beam;as the preload value increases,the hysteresis strain of the CFRP increases,and the flexural capacity increases.The increase of the number of reinforcement layers will lead flexural capacity of the beam,but the degree of improvement does not increase exponentially;the unloading strengthening has a higher flexural capacity.Before the strengthening,to improve the strengthening effect,the structure should be unloaded as much as possible to reduce the hysteresis strain of the CFRP,so that the CFRP enters the working state as soon as possible with the steel bars.Considering the influence of the quadratic loading,the calculation formula of CFRP hysteresis strain of the beam under unloading and holding is deduced.According to different failure types,the corresponding calculation formula of flexural capacity and the limit configuration rate are derived.Combined with the experimental data,the validity of the formula is verified,which can be used as reference for future research and practical application.