Numerical Simulation Of Reinforced Concrete Beam Based On Damage Equivalent Elasticity

Reinforced concrete is the most widely used building material in various industrial and civil buildings.The use of finite element software in the simulation of reinforced concrete structure has gradually become the main means to research the structural performance with the increasing complexity of building structure.However,it is difficult to consider both the details and the overall mechanical properties of large building structures by finite element technique.In this paper,the unit cell model of transverse isotropic reinforced concrete considering tensile damage was developed from the perspective of meso-mechanics of composite materials.The four-point bending tests of reinforced concrete beams were simulated by the complied USDFLD program.And the main contents and conclusions are as follows:(1)The unit cell model of the transverse isotropic reinforced concrete considering the tensile damage was established based on the micro-mechanics and homogenization theory.The isotropic equivalent properties satisfying the transverse isotropic properties were obtained by the Mori-Tanaka theory of fiber reinforced composites in elastic stage.And the axial equivalent performance of unit cell model for reinforced concrete after cracking and interface debonding was derived by ACK theory including random cracking.And the results show that the axial equivalent performance of unit cell model decreases with the cracking of concrete,and it tends to be stable after cracking saturation.In addition,the analysis of the parameters for the equivalent properties in each direction under different ratio of steel bar shows that the theoretical analysis model of the elastic properties of reinforced concrete is reasonable.(2)Considering the tensile damage,a user subroutine USDFLD was compiled on the basis of the equivalent theory of reinforced concrete The simulation of a unit model under uniaxial loading and unloading shows that the tensile damage process of reinforced concrete with the equivalent properties can be preferably described by this damage analysis model.And the secant modulus under different tensile degrees are consistent with the theoretical values,which proves the feasibility and effectiveness of the USDFLD program.(3)Eight reinforced concrete beams with different reinforcements were conducted in four-point bending test.The results show that the bending stiffness and the ultimate load increases with the increase of reinforcement ratio in elastic stage.The bearing capacity of bending section in the beam is relatively weak with the low reinforcement ratio of longitudinal reinforcement.It indicates normal section failure in the pure bending section.The cracks mainly appear in the pure bending section of the beam and are basically perpendicular to the axis of the beam.The concrete is finally crushed at the top of the span in the beam.The bearing capacity of bending section in the beam is relatively strong with the high reinforcement ratio of longitudinal reinforcement.It indicates oblique section failure in the shear section.The diagonal cracks on both sides of the four-point bending beam are rich,and the main diagonal cracks break through the beam.(4)An improved finite element model of reinforced concrete beam was established based on the damage analysis model of reinforced concrete unit cell and compiled USDFLD.The steel bar and its surrounding concrete were equivalent to a transverse isotropic body.The sensitivity analysis of the related mesoscopic parameters in this model was carried out by the unit cell model.The reasonable value range of mesoscopic parameters was given by comparing with the experimental data.The four-point bending beams were simulated by this improved model and a typical embedded model respectively,which explained the mesoscopic failure mechanism of reinforced concrete beams under four-point bending test from a meso level.The validity and accuracy of the finite element simulation based on the equivalent properties of reinforced concrete are verified by comparing with the test results.