Structural Response And Numerical Simulation Of Reinforced Concrete Beams Under Impact Loading

As a multi-phase composite,the difference of physical characteristics of each component and the complex stress analysis of the aggregate and the mortar in the concrete,making it difficult to study the fracture mechanism of the concrete.Concrete have been widely used in engineering field for over 100 years due to the good thermal insulation and compression resistance.Under the external loading,new cracks generated from the existing defects,microporous holes and other damage in concrete result in large cracks of the building,which causes huge dangers to the national defense engineering,industrial buildings and bridges,and brings property losses for the national economy.The steel bar in the concrete matrix inhibits the produce and expansion for the cracks effectively when the concrete structure is damaged.Besides,the stress analysis of the contact surface between the steel bar and concrete is still a hot issue these years.Because of the strain rate effect,the failuremode of reinforced concrete beams changes as the increase of the impact velocity and change of the ratio of reinforcement.The stress analysis of reinforced concrete structures under unexpected conditions,such as explosion,impact and other non-design loads,has been widely concerned by scholars and engineers.It is very necessary to study the impact resistance of reinforced concrete structures and the failure modes under dynamic loading.In this paper,three point bending dynamic experiment and numerical simulation for the beam with prefabricated cracks under different heights were carried out to study the structural response and the failure mode of the beam.The main works are as follows:The specimens with prefabricated cracks were artificially constructed,and the impact test of concrete beams was carried out by the DHR-9401 impact test machine,and the high-speed video tracking was carried out with DIC.The deformation and failure modes of the beams under four different impact heights were analyzed.By comparing the bearing capacity of the specimen,the change of the crack strain at the tip of the precast concrete and the strain of the steel bar,the resistance bearing capacity and the change of the failure mode of the beam were analyzed.The experimental results show that the failure mode of the beam is changed when the impact height is greater than 60 mm,and the macro crack on the surface of the beam becomes clearer.At the same time,the time curves for the impact forces show a different trend of shockdevelopment.And the strain of the steel bar gradually tends to the stable value,which shows the effect on tensile strength and crack resistance of concrete is gradually weakened.Based on the ABAQUS software,the damage and fracture model of concrete and the trilinear model of steel bar were introduced to carry out numerical simulation analysis.Compared with the maximum of impact force and the response time,the validity of the model was verified.Compared with the other experimental results,the time curves for the impact force and the mid span deflection were in good agreement with the simulation results.The failure mode of the beam gradually changes from the bending failure to the shear failure as the increase of the impact velocities,which proves that the model has a certain universality.On the basis of this model,the cross section area of the steel bar in the finite element model are changed to change the reinforcement ratio of the beam.And then the influence of the reinforcement ratio on the bearing capacity,the resistance to deformation and the failure mode of the beam under different impact speeds is discussed.The simulation results show that with the decrease of the reinforcement ratio and the increase of impact speed,the fracture mode of beam gradually changes from bending failure to shear failure.