Experimental Study On Flexural Performance Of Reinforced Concrete Beams Strengthened With Near Surface Mounted BFRP Bars

In recent years,more and more attention has been paid to the maintenance and reinforcement of reinforced concrete structures in order to reduce environmental pollution and waste of resources caused by construction waste.As a new type of reinforced composite material,basalt fiber reinforced polymer(BFRP)has the advantages of light weight,high strength,high temperature resistance,and corrosion resistance.It has broad application prospects in the reinforcement of engineering structures.Compared with the traditional EB technique,the near surface mounted(NSM)technique has the superiorities of small workload,strong impact resistance,corrosion resistance and good fireproof performance.At present,the research on reinforced concrete(RC)beams strengthened with NSM BFRP bars is still in its infancy.There is little research on the reinforcement effect and failure mechanism of BFRP bars.In order to clarify the reinforcement effect of BFRP bars and the specific role of the technology in engineering practice,it is necessary to further study it.This paper designed and produced seven RC beams.The test considering tensile reinforcement ratio,amount of BFRP bars and pre-loading.By collecting test data and observing the test phenomena,the bending performance of reinforced concrete beams strengthened with BFRP bars was studied as follows:(1)The experimental research shows that: The NSM BFRP bars can significantly enhance the bearing performance of reinforced concrete beams.The reinforcing effect is mainly manifested after the yield of longitudinal bars.The failure modes of the strengthened beam are bending failure and bond failure.The pre-loading can easily peel off the concrete protective layer at the end of the BFRP bar.The BFRP bars have good crack-resistance to the strengthened beams,which can effectively delay the development of cracks and reduce the crack spacing and width.(2)In view of the basic theory of calculation of flexural capacity of reinforced concrete beams,the conjugated beam method is used to propose the theoretical model of the load-carrying capacity and the calculation formula for the mid-span deflection of the reinforced concrete beam strengthened with NSM BFRP bars.The load-deflection calculation program for full-range analysis of the reinforcement beam loading process has beendeveloped.The results show that the calculated values agree well with the experimental values.(3)Based on the Teng & Zhang interface model and according to the analytical formulas of shear stress and normal stress at the interface between BFRP bars and concrete,the correction method for the bond-slip of the RC beams strengthened with NSM BFRP bars is given,debonding capacity calculation formula of BFRP to concrete is deduced.The calculation results show that: The problem of bond-slip is prevalent in reinforced beams.The relative slip of the BFRP bar-concrete interface reduces the ultimate load of the strengthened beams,which is usually prominent after the steel bars yield.The stress at the end of the BFRP bars is concentrated,and the peeling failure is easy to occur.The peeling bearing capacity of the strengthened beams is mainly affected by the bonding length of the BFRP bars and pre-loading.(4)The accuracy of the calculation model of this paper is verified by referring to the experimental data of related research at home and abroad.The results show that: This model can accurately predict the characteristic load and mid-span deflection of reinforced concrete beams strengthened with NSM FRP.The predictions of bond slip and peeling load agree well with the experimental values.It has wide applicability in the the full-range analysis of RC beams reinforced with NSM FRP.