Study On Interfacial Bond Behavior Of FRP Near Surface Mounted Systems

The innovative retrofitting technique of strengtnening concrete structures with near-surface mounted(NSM)fiber reinforced polymer(FRP)has attracted incresing attention from researchers.FRP bar splitting induced by interfacial bond failure,adhesive splitting and other reasons has always been a problem needed to be solved in the NSM FRP systems.An innovative anchorage strengthening method is proposed in this aticle.Based on this method,the experimental study was carried out.In the first part,an experimental program aimed to test the interfacial shear strength between strengthening rib and FRP bar is presented.The results show that the interfacial shear strength is relatively high and the anchorage strengthening method represents a sound alternative.Besides,the optimum parameters of strengthening rib were determined through comparative analysis of the experimental results.In the second part,36 direct pullout specimens and 12 beam pullout specimens were designed and tested in order to study the effect of bond length,the number of strengthening rib,groove geometry,adhesive type,FRP bar type and test method on the bond behavior of NSM FRP systems.The results show that the strengthening rib could improve the bond performance of FRP bar,and the effect of strengthening rib on BFRP bar was smaller than that of CFRP bar.Increasing the dimension of groove could elevate the ultimate load of NSM FRP bar.Arc-shaped geometry could relieve the stress concentration of groove.For beam pullout specimens,detachment of concrete cover may happen when the loading end of concrete block is unconstrained.Wire mesh-motar was designed to strengthen the concrete cover in the last part,and 12 specimens strengthened with wire mesh-motar and 8 unstrengthened specimens were tested in order to study the effect of wire mesh-motar.The results show that wire mesh-motar reinforcement has effective strengthening effect on the existing concrete cover.Wire mesh-motar reinforcement could provide strong constrain effect on the filling material,elevating the ultimate load of NSM FRP bat The strengtnening effect of wire mesh-motar reinforcement on BFRP bar specimens was smaller than that of CFRP bar specimens,and the strengthening effect was better when filling motar as the adhesive.The thickness of wire mesh-motar has no effect on BFRP bar specimens with epoxy resin adhesive.For the specimens with motar adhesive,the thicker wire mesh-motar has better strengthening effect.A simplified bond-slip relationship was proposed based on data simulation of experimental results.Through solving bond differential equation,a bond strength model was estibilished,and the feasibility of the model was confirmed by the experimental results.A finite elment(FE)model was estibalished to study the detachment failure of concrete cover,and the rationality of the FE model was confirmed by the experimental results.