3D Numerical Simulation Of Reinforced Concrete Beams Under Dynamic Loading-influence Of Interface Properties And Loading Rates

Reinforced concrete structures have been widely used in the field of construction engineering in China.Reinforced concrete（RC）is a heterogeneous multiphase composite material composed of matrix,aggregate,steel bar and the interface transition zone between steel bar and matrix.Among them,interface transition zone is the key for the steel bar and the matrix to work together.As a stress transferring bridge between the matrix and the steel bar,the interface transition zone combines the steel bar and concrete with greatly different properties as a whole,which is a significant part of the reinforced concrete.The engineering practice shows that interfacial transition zone is the first damaged area in reinforced concrete components.Therefore,the interfacial properties affect the overall macroscopic properties and damage mechanism of the material to a great extent.In practical engineering,RC components are inevitably subjected to impact loads with characteristics of short duration and high peak value.The stress,strain and fracture mechanism of the RC components are very complex under dynamic load,and interface exists inside the material with special properties and tiny size.In the aspect of fully revealing the influence of interfacial properties on cracking failure mechanism of materials,physical experiment method has limitations and there are few related research achievements at present.Numerical simulation method can make up for the limitations of physical experiment method.It is of great significance to study the damage mechanism and interface mechanical behavior of RC under dynamic load by using numerical simulation method.In this paper,in view of the effects of interfacial strength,interfacial elastic modulus and dynamic loading rate on the mechanical properties of RC beams,the physical and mechanical properties of the three-point and four-point bending beams under three-dimensional dynamic load were simulated by using RFPA^3D-Dynamic analysis software,on the premise of considering the heterogeneous distribution of materials in each phase of RC beam.The simulation of the whole process from crack initiation,propagation to instability failure is realized.The effects of interfacial elastic modulus,interfacial strength and dynamic loading rate on the performance of RC beams are numerically studied.（1）Taking the elastic modulus of the interfacial transition zone as a variable,a three-dimensional calculation model of the three-point bending RC beam is established under interface control,and the effect of the interfacial elastic modulus on the performance of RC beam under dynamic load is studied.The results show that the variation of interfacial elastic modulus has significant influence on the final failure mode and failure process of the specimen.With the increase of the specimen interface elastic modulus,the failure mode of the specimen gradually changes from bending tensile failure with bending crack to shear failure with oblique crack.Meanwhile,the variation of interface elastic modulus also leads to the change of the acoustic emission behavior of the specimen,representing the change of the energy dissipation capacity of the specimen.The energy dissipation capacity of the specimen increases first and then decreases.The peak load increases first and then decreases with the increase of interfacial elastic modulus during the failure process.（2）Taking the strength of interfacial transition zone as a variable,a three-dimensional model of four-point bending RC beam is established under interfacial control.The effect of the interfacial strength of RC beam on the performance of reinforced concrete under dynamic load is studied.The results show that the variation of interfacial strength has a great influence on the final failure mode and failure process of the specimen.With the increase of the specimen interfacial strength,the failure mode of the specimen gradually changes from bending tensile failure with bending crack to shear failure with oblique crack.At the same time,with the increase of interfacial strength,the maximum accumulated acoustic emission energy of the specimen increases first and then decreases.The peak load increases with increased interfacial strength.When the interfacial strength increases to the same as the matrix strength,the peak load of the specimen does not increase but gradually tends to be stable.（3）Taking the loading rate of dynamic load as a variable,three groups of four-point bending numerical models were established under dynamic loading.The effect of dynamic loading rate on the mechanical properties of RC beam specimens with different interfacial strength was simulated respectively.The results show that the influence of loading rate may be different with different interfacial strength.The change of loading rate at low interfacial strength has limited influence on the failure mode of the specimen.However,for the specimens with medium and high interfacial strength,the loading rate has a great influence on the failure mode,especially for the specimens with medium interfacial strength.The change of loading rate has an effect on the failure velocity of the three groups of specimens.The peak load of the specimen increases first and then decreases with the increase of the loading rate,but the loading rate corresponding to the maximum peak load of the specimen with different interfacial strength is different.The accumulative acoustic emission energy increases with the increase of loading rate,and the lower the interfacial strength is,the greater the accumulative acoustic emission energy will be.