Research On Shear Performance Of BFRP Reinforced Concrete Beams

In recent years,premature deterioration of concrete structures caused by steel corrosion has been reported in many investigation papers at home and abroad.How to solve the durability problem of concrete structure caused by steel corrosion has become a major issue that domestic and foreign scholars must face.The application of FRP bars is one of the effective ways to solve a series of durability problems caused by steel corrosion.FRP bar has the advantages of light weight,high strength,good corrosion resistance,non-magnetic insulation and so on.It can be used in harsh environment which is vulnerable to various environmental factors.BFRP is a new type of FRP and its mechanical properties is between GFRP and CFRP,but it has a higher cost performance.At present,the domestic research on the structural performance of BFRP reinforced concrete beams mainly focused on the flexural performance of normal section,and the research on shear performance is insufficient.Therefore,this paper studies the shear performance of BFRP reinfored concrete beams through experimental investigation and numerical simulation.This research designed and constructed 19 specimens based on the experimental variables such as stirrup type,reinforcement ratio of longitudinal main bars,longitudinal reinforcement type and shear span to effetive depth ratio.The shear performance of BFRP beams was investigated systematically and thoroughly by three-point loading test.Based on the experimental results,the finite element software DIANA was also used to model the specimens and carry out a non-linear numerical simulation.The experimental results were verified,and the shear mechanism was further investigated.Finally,based on the experimental investigation and numerical simulation results,the shear bearing mechanism of BFRP beams was revealed.\Wthin the scope of this study,the following useful conclusions are drawn:(1)About failure modesThe experimental results show that,when the longitudinal reinforcement is BFRP,the stirrups are BFRP or steel bar reinforcement,and the reinforcement ratio is reasonable,the specimens fails in shear compression failure.Compared with the BFRP stirrups,the post-peak failure of specimens reinforced with steel bar stirrups is relatively ductile.For specimenss reinforced with BFRP main bars and without web reinforcement,diagonal tension failure occurs when shear span to effective depth ratio are 2.5 and 3.5.(2)About stiffnessThe longitudinal reinforcement elastic modulus has significant effect on the pre-diagonal-crack stiffness.For specimens containing longitudinal reinforcement with smaller elastic modulus,the pre-diagonal-crack is obviously smaller.The reinforcement ratio of longitudinal main bars,types of stirrups and types of longitudinal reinforcement all affect the post-diagonal-crack stiffness,the post-diagonal-crack stiffness increase with the increase of reinforcement ratio of longitudinal main bars,the elastic modulus of longitudinal reinforcement,and the elastic modulus of sirrups.(3)About shear capacityThe shear capacity increases with the increase of reinforcement ratio or elastic modulus of longitudinal reinforcement.The reasons are as follows:the constraint effect on the progress of diagonal crack opening decrease with the increase of the ratio of longitudinal reinforcement or elastic modulus of longitudinal reinforcement,and furthermore result in the increase the shear force transferred by the interlock action by aggregate and the shear force borne by uncracked concrete;and at the same time,the inclination angle of main diagonal crack tends to decrease,the number of stirrups intersecting the main diagonal crack is increased,and the"arch mechanism"bears shear force and"truss machine"at ultimate state is raised.(4)About the loadcarrying mechanismThe numerical simulation results show that for the same reinforcement ratio of longitudinal main bars,the greater the stirrup elastic modulus is,the faster the shear resistance carried by"truss mechanism"increase during the loading process.At ultimate state,the"truss mechanism" bears more shear resistance than the"arch mechanism".For the specimens using the same stirrups,the shear resistance carried by the"arch mechanism"and"truss mechanism"increase with the reinforcement ratio of longitudinal main bars;For the specimens using the same stirrups and the reinforcement ratio of longitudinal main bars,the shear resistance carried by"arch mechanism"increase with the increase of the elastic modulus of longitudinal steel bars,(5)About quantitative evaluation of shear capacity of design codesBritish codes overevaluate the shear strength tof BFRP beams in this research,while American codes and Japanese codes provide under evaluation results.Overall,the Canadian codes provide the most accurate prediction.