Flexural Behavior Of High Strength Concrete Beams Strengthened With Prestressed CFRP Under Sustained Load

Carbon fiber reinforced polymer(CFRP)has the advantages of high strength,light weight,convenient and simple operation,hard to be corroded,acid and alkali resistance,etc.,which solves many problems encountered in the reinforcement of concrete structures.However,from the practical application point of view,there are some problems in strengthening concrete beams with CFRP,such as large deformation is needed to play its high-strength characteristics,resulting in its low utilization rate;the cracking load and yield load of strengthened beams are not significantly improved in the use stage.In view of these problems,it can be effectively solved by applying prestress to CFRP.At the same time,in the actual reinforcement process,the concrete members are always under the continuous load,that is,there is the initial test bending moment.In order to simplify the calculation,a large number of experimental studies have not considered the initial bending moment of the component,so this simplification makes the theoretical calculation of the bearing capacity larger than the actual bending capacity of the component.When the continuous load of the reinforced structure is at a large value,it is unsafe.Based on the above considerations,it is of great significance to study the influence of the magnitude and time of sustained load on the strengthening of high-strength concrete beams with prestressed CFRP.On the basis of the National Natural Science Foundation of China(51378089),a total of36 test beams were produced according to needs,and the self-designed load-bearing device and prestressed tension device were used to apply load and prestress to the reinforced beam.The pre-stress level is set to 0%,7.5%,15%,and 30% of the standard value of the tensile strength of the carbon fiber cloth,and the load rating is 0%,30% of the ultimate bearing capacity of the reinforced concrete beams not reinforced with carbon fiber cloth.And 60%,and the holding time is 0 days,15 days,30 days and 45 days,respectively.The effects of load level,load time and prestress level on the flexural performance of CFRP reinforced high-strength concrete beams were studied.The study mainly reached the following conclusions:(1)The flexural performance of CFRP-strengthened high-strength concrete beams under continuous load is studied.The results show that the failure form of CFRP-strengthened beams under continuous load is mainly interface peeling damage.The development of cracks makes the average width and length of cracks larger.In addition,the presence of continuousloads significantly reduces the cracking load,F0.2 load,ultimate load,yield load,ultimate deflection and CFRP strain peak of CFRP strengthened beams,and the load rating The higher,the longer the holding time,the worse the bending resistance of the reinforced beam,and the lower the CFRP utilization rate.(2)The flexural performance of high-strength concrete beams after CFRP reinforcement under different prestress levels was studied.The results showed that the failure forms of prestressed CFRP reinforced beams were all peeling failures caused by central cracks.The cracking load and ultimate load reduce the ultimate deflection,and the higher the prestress,the stronger the bearing capacity and the greater the flexural rigidity,giving full play to the high-strength characteristics of CFRP.(3)The flexural performance of prestressed CFRP reinforced high-strength concrete beams under continuous load is studied.The results show that the failure form of prestressed CFRP reinforced beams under continuous load is mainly the interface stripping failure of the bending shear section,and the existence of continuous load Significantly reduce the effect of prestress on the cracking of concrete,significantly change the failure form of reinforced beams,and significantly reduce the cracking load,F0.2 load,ultimate load,ultimate deflection and CFRP strain peak of prestressed CFRP reinforced beams,and The higher the holding level,the longer the holding time,the lower the bearing capacity,the lower the bending stiffness,and the lower the CFRP’s restriction on concrete.(4)The formula derivation and calculation of flexural capacity of beams strengthened with CFRP are studied.The results show that the calculated value of flexural capacity is consistent with the actual value in the test process,and the calculated value is partial to safety.The calculation formula of flexural capacity can be applied.