Study On The Static Behavior Of Near Surface Mounted CFRP Strengthened Beams With Non-Prestressed Bonded Ends

After nearly ten years of in-depth research,the near-surface-mounted(NSM)prestressed carbon fiber reinforced polymer(CFRP)-strengthened reinforced concrete beam has become the mainstream solution for the restoration and reconstruction of aging infrastructure structures.However,without permanent anchors,the reinforced structure is prone to brittle debonding failure at the bonded end of CFRP,leading to premature failure of the structure before reaching the expected bearing capacity.At present,most domestic and foreign pre-stressed NSM CFRP-reinforced beam end debonding suppression methods are the addition of externally attached anchoring devices,which generally have defects such as complicated processes,increased costs,and damage to the original structure,resulting in unsatisfactory anchoring effects.In view of this,13 prestressed NSM CFRP strengthened reinforced concrete beams with non-prestressed end bonding section were designed.The effects of bond length of non-prestressed and bond length combination of prestressed and non-prestressed sections on the mechanical behavior,failure modes and stress transfer behavior of reinforced beams were studied.The optimal length of non-prestressed end bond section of prestressed NSM CFRP system was obtained based on experiment.In addition,the end debonding strength model of the NSM CFRP reinforced beams non-prestressed end bond section was proposed,and the test results were used to verify the rationality of the model.The main results can be listed as follow:1.The non-prestressed end bonding section provided on the prestressed NSM CFRP reinforced beam can significantly increase the bond end cracking load and ultimate load of the reinforced members,and at the same time can make up for the residual deformation capacity of the member reduced by the application of prestress,thereby delaying and suppressing the debonding failure of the prestressed NSM CFRP strengthened reinforced concrete beams happened.2.When the total bonding length is not limited,the load-bearing performance and deformation performance of the reinforced member with non-prestressed endbonding section will increase with the extension of the non-prestressed bonding section,but there is an upper limit of the effective bonding length.After the length of the non-prestressed section exceeds the upper limit,the performance improvement of the member is limited.3.When the total bonding length is limited,extending the non-prestressed bonding section will cause the bond end cracking load and ultimate load of the reinforced members to increase first and then decrease,so there is an optimal combination of prestressed section and non-prestressed section.Under the experimental parameters of this paper,the upper limit of the effective length of the non-prestressed bonding section at the end of the prestressed NSM CFRP system is 300mm.4.Under the condition that the total bonding length is limited,when the length of the non-prestressed bonding section provided at the end does not exceed 100mm,the failure mode of the component tends to be that of the prestressed NSM FRP reinforced member;when the length of the non-prestressed bonding section meets the upper limit of the effective bond stress transfer length(300mm),its failure mode and load carrying capacity are equivalent to the non-prestressed NSM CFRP reinforced beams of the same total bond length.5.The calculated values of the existing non-prestressed NSM CFRP reinforced beam end debonding strength model and the test values of the NSM CFRP reinforced specimens with non-prestressed end bonding section in this article are generally in good agreement.However,when the value of the total bonding length changes,there is a large error.