The Static And Fatigue Load Behavior Of Reinforced Concrete Beams Strengthened With NSM Prestressed CFRP Strips

Along with the increment of traffic volume and deterioration of the environment,some serious damage degradations of carrying capacity appeared among a large number of bridges in our country.Therefore,it is necessary to finish the reinforcement to ensure the safety of these bridges.Fiber Reinforced Polymer(FRP),as a new engineering material,has been widely investigated and used in the civil engineering industry since this material possesses mechanical properties of light weight,high strength and excellent durability performance.It is extremely difficult for a traditional technology of Externally Bonded(EB)FRP to make full use of its high strength performance of the FRP.And the interface between the externally bonded FRP and concrete could be debonded easily.But another reinforcing technology,called the prestressed Near-Surface-Mounted(NSM)FRP reinforcement techology,could restrain the dedonding between the FRP and concrete.At the same time,the prestressed FRP could improve the stress status of the previous structures effectively,improving its utilization rate of the FRP material.Besides,the NSM technology could also provide anchorage for the prestressing force,reducing the expenses of some mechanical anchorage devices.So this sort of technology has some strikingly technological and economic advantages and widespread prospect of application.At present,the reinforcement technology using prestressed NSM FRP still lacks of enough investigating works among domestic and overseas areas.In view of this,a series of static and fatigue experiments of 9 prestressed NSM FRP reinforced RC beams were carried out in this paper.Considering the different prestress levels,bond length and non-prestressed bond portions,the mechanical properties and failure modes of specimens were investigated.The results show that:1)the enhancement of prestressed levels could improve the mechanical properties of structures a lot,increasing their intermediate crack load and steel rebars yield load.But the end debonding failure caused by very high prestressed levels could result in obvious decline of the ultimate load;2)With the increment of bond length,the crack load of end concrete of the specimens,the horizontal crack load and the ultimate load would increase,and it exerts an obvious impact on their failure modes;3)The ultimate carrying capacity,the crack load in the prestressed end,the ultimate carrying capacity in the prestressed end,the crack load in the adhesive end as well as the ultimate carrying capacity in the adhesive end will increase frist and then decrease along with the length increment of non-prestressed portions.;4)That adding the non-prestressed bond portions makes the failure modes change from the debonding failure of groove bottom into the concrete end debonding,and then it shifts into concrete crushing failure?Besides thoes,based on the results of static experiments,the fatigue experiments of three beams were carried out.Their fatigue mechanism and failure modes,considering the variables of bond length and non-prestressed bond portions,were investigated.The results show that:1)That increasing the bond length of FRP and adding non-prestressed bond portions could enhance the fatigue lifespan of reinforcement specimens.;2)With the increment of adhesive length,the fatigue model of reinforing beams changes from the concrete cover separation failure to the separation failure of the concrete groove bottom interface,and their fatigue lifesan improves obviously.3)That adding the supplement of non-prestressed portions could effectively suppress developing cracks in the end concrete under fatigue load,avoid the separation failure model in the end concrete,and improve the fatigue lifespan of reinforcing beams a lot.