Study On Local Bond-Slip Behavior Between NSM FRP Bars And Concrete Under Different Loading Form

Building structure in service, due to the joint action of internal and external factors, declined in bearing capacity or use function that can not satisfy the normal use requirements, these structures are inevitably will face issue of strengthening. FRP bar is a new style composite material that possesses nicer mechanics and durability. NSM(near-surface-mounted)FRP reinforcement is one of the latest and most promising strengthing techniques, has gradually become research focus in the field of concrete structure strengthening. The bonding performance of FRP bar and concrete is one of the basic mechanic properties of the FRP reinforced concrete structures; it also is one of the key techniques about designing and spreading this structural.This topic, studying on bond-slip behavior of concrete with NSM FRP bars, expects to provide a reference for research and application of NSM reinforcement techniques.This paper study the failure mode of the concrete reinforced with NSM FRP bars specimens were tested in direct pullout. Analysis of the parameters about the diameter of FRP bars; Bond length and the type of FRP bars. The test shows that the concrete reinforced with FRP bars specimens have four failure modes:debonding failure between FRP bars and adhesive interface; debonding failure between concrete and adhesive interface; tensile failure of FRP bars and split of adhesive. The parameters shows that when the bond length were same, the maximum bond stress appears in d=10mm specimens. When the FRP bars have the same diameter, the bond stress of specimens with BFRP bars increased with the bond length increased and the bond stress of specimens with GFRP bars decreased with the bond length increased. When the bond length and diameter of FRP bars were same, the specimens with GFRP bars have maximum bond stress.Based on the analysis and fitting of experimental curves, the bond-slip constitutive law of concrete reinforced with FRP bars was established in this paper. On the basis of those, the formula of minimal development length of FRP bars was presented.The pullout test specimens were numerical analysis with ABAQUS. Compared with the simulation and the test results, it shows that the simulation curves have a good agreement with the test curves, and this verfies the correctness of the mode. On the basis of those, the distribution curves of strain and bond stress about FRP bars in the bonded area were analyzed.Experimental study on the RC beam with FRP bars specimens. Analysis of the parameters about the diameter of FRP bars; Bond length and the type of FRP bars. The test shows that the RC beam with FRP bars specimens have three failure modes:Completely splitting of the epoxy adhesive; local debonding of the epoxy adhesive and FRP reinforcement rupture. The parameters shows that when the bond length were same, the maximum ultimate load appears in d-10mm specimens. When the bond length less than 400mm, the ultimate load of specimens with FRP bars increased with the bond length increased. When the bond length more than 400mm, the ultimate load of specimens with FRP bars decreased with the bond length increased. When the bond length and diameter of FRP bars were same, the specimens with GFRP bars have maximum ultimate load if the bond length less than 200mm and specimens with BFRP bars have maximum ultimate load if the bond length more than 200mm.