Study Of High Strengthened Concrete Beam With Prestressed CFRP Under Hygrothermal Environment

In order to meet the rapid development of the economy and technology,various types of buildings across the country have risen rapidly,and civil engineering has developed vigorously.High-strength concrete is widely used in the field high-rise buildings and large-span structures due to its high strength and compactness.However,with the lapse of time,some existing houses and bridge buildings are gradually unable to meet the requirements of use due to natural aging or corrosion.If these buildings are demolished and rebuilt,serious economic losses and unnecessary waste will be caused.The most effective solution is to strengthen the structure.CFRP materials have attracted many scholars’ attention because of their high tensile strength,good corrosion resistance and light weight.They have brought new opportunities for the development of concrete reinforcement engineering.Carbon fiber reinforced concrete structures still works under the influence of various erosion environment during the service.Therefore,the performance of the reinforced structure in a complex environment has become an important issue to be studied.The influence of prestressing grade,temperature and beams’ size on the flexural behavior of the strengthened test beams is analyzed.The main research results are as follows:(1)The effect of CFRP prestress level change on the flexural behavior of strengthened test beams is studied.The results show that CFRP is applied to the bottom of high-strength concrete beam will significantly increase the cracking load and ultimate load of test beams.The higher the CFRP prestressing level is,the more obvious the carrying capacity improvement effect.Prestressed CFRP can effectively inhibit the generation and development of concrete cracks,reduce the deformation of test beams,improve the bending stiffness of test specimens,and give full play to the high strength performance of CFRP.The failure mode of the test beam is mainly the peeling failure.The higher the CFRP prestressing level is,the more concrete aggregates are stuck under the peeling failure.(2)The flexural behavior of prestressed CFRP reinforced high strength concrete beams under hygrothermal environment is studied.The results show that after the action of hot and humid environment,the cracking load and ultimate load of the strengthened test beam are reduced to different degrees.The higher the temperature is,the greater the decrease is.The higher the CFRP prestressing level is,the more significant the bearing capacity of the test beam decrease is.Under the same prestressing level,as the temperature increases,the aggregate of CFRP surface is gradually reduced when the test beam is peeled off.The effectof prestressing exacerbates the deterioration of the interface bonding performance of the hygrothermal environment.The position of the failure surface gradually shifts from the concrete protective layer to the resin adhesive layer after hygrothermal action.(3)The changes in flexural properties of test beam with different sizes are studied in hygrothemal environment.The cracking load,ultimate load,ductility coefficient and CFRP strain distribution of the test beams are comparative analyzed.The results show that the change of the test beam size has no significant effect on the prestressed CFRP reinforcement effect under hygrothermal environment.The change of beams’ size makes the test beam failure mode different.The failure mode of the test beam is mainly the interface peeling damage caused by the middle crack,and the other peeling damage is caused by the bending shear crack.