Test Study On Bond Behavior Between Plain Bar And Concrete Under Dynamic Tensile Loading

With the extensive use of reinforced concrete structures,the mechanical properties of reinforced concrete structures under blast impact are getting more and more attention.Among them,the dynamic bond performance of reinforced concrete has been confirmed as the main research objects.The bonding interface between the rebar and concrete is destroyed due to the difference of deformation amounts,and the strength of the bonding interface has a great influence on the overall strength and the damage mode of the concrete structure.In this paper,the relationship between bond strength and strain rate was obtained by pulling out test of the center of plain-bar reinforced concrete with different strain rates depending on designing a test scheme for dynamic bond performance of reinforced concrete.The main research contents and results include:(1)Designing and processing the loading device which is suitable for the central pullout test of reinforced concrete based on the MTS universal testing machine and Zwick/Roell HTM5020 high speed drawing machine of Hopkinson rod laboratory of Ningbo university,Measuring the actual stress of steel bars through strain gages,and using the digital image correlation(DIC)measurement technique to correct the displacement data of the steel bars to obtain the actual slip amount of the steel bars.The test scheme is suitable for general dynamic pull-out tests.(2)Conducting several sets of quasi-static and dynamic tests which's test pieces is of the same size,the test results of bond-slip of light round reinforced concrete at different strain rates have been obtained,the damage of the concrete is observed and analyzed.The results show: the bonded-slip relationship of reinforced concrete with round steel bar could be divided into four stages: sliding section,approximate platform section,descending section and residual section.Increased strain rate would result in less damage to the bonding interface;the ultimate bond stress linearly increases with strain rates,locally,the quasi-static fluctuation was not significant,but the linear relationship was very obvious under dynamic loading.(3)The formula for the general relationship of the slip-up section of the bonding-slip curve of reinforced concrete is obtained by fitting the data,it lays the foundation for subsequent research.(4)Establishing a 2D model of the pullout test for reinforced concrete which with plain bar based on cohesive unit of ABAQUS finite element software,calculation and analysis shows that: the tensile stress in concrete is mainly concentrated near the loading end of the reinforcement;the adhesive force will be lower with farther away from the actual loading surface.