Shear Test Research Of Concrete Under Lateral Pressure And Application

At present,concrete structures are widely used in housing,infrastructure,ports and aviation because of their stable mechanical properties,good economy and good aging resistance.During the use of concrete structures,there are always various diseases(such as material corrosion,weathering,vehicle overload,uneven settlement of foundation,etc.),which lead to the structure entering damage and destruction state prematurely,and eventually may cause the whole structure to collapse suddenly.Among them,the phenomenon of cracking and failure of components and structures is common due to insufficient shear strength of concrete.Shear strength is not only an important mechanical index of concrete,but also an important object of numerical simulation results.Therefore,shear design is an important part of reinforced concrete component design.For example,near the support of concrete beams or short beams,concrete brackets,tunnel lining and so on.In this kind of research,the interface shear spring should be determined according to the shear strength of concrete and the stressstrain softening curve.However,unlike uniaxial tension and compression tests of concrete materials,the shear mechanical properties(especially compression-shear mechanical properties)of concrete materials have not yet formed a standard method and process,and there are no corresponding provisions in relevant specifications.Therefore,it is necessary to systematically study the shear strength and stress-strain curves of concrete materials in order to provide reference and basis for the mechanical analysis of concrete shear members.As concrete is a typical anisotropic three-phase composite material,its mechanical properties are determined by the interaction of internal components.Based on Mohr-Coulomb strength criterion,this paper studies the shear failure mechanics and summarizes the stress-strain constitutive model of concrete under compression-shear failure.According to this constitutive model,the macro-cracking failure of reinforced concrete simply supported beams is simulated.Based on the meso-structure of concrete and the heterogeneity of material,the damage mechanism of concrete under meso-compression and shear is studied by combining experiment with numerical simulation.Major innovative research efforts include:1)Based on the existing shear tests at home and abroad,a set of suitable reinforced concrete Z-shaped specimens and shear fixtures suitable for specimens are designed,so that they can shear slip and crack under lateral pressure in the axial direction.Through the compression-shear test,the shear cracking behavior of concrete with different strength under different lateral pressures is obtained.Finally,the shear displacement curve fitted by statistical test data determines the cohesion c and internal friction angle_of concrete.The intercept represents cohesion c,and the slope represents internal friction angle_.The modified anisotropic Mohr-Coulomb criterion of concrete is established as a simplification of concrete.Constitutive model for macro-simulation of supporting beam.2)Based on commercial finite element software ABAQUS,a two-dimensional meso-numerical model of concrete Z-type test is established.In this model,Monte Carlo method combined with occupancy elimination algorithm is used to realize the random placement of diverse aggregates,and the mechanical parameters of each meso-element are assigned based on probability distribution and random assignment method.In order to simulate the whole process of the initiation,evolution and cracking of random cracks,the cohesive element user subroutine developed by the team was used to insert the cohesive element into the interface area except the aggregate element based on the traction-separation constitutive relationship,and the Mohr-Coulomb yield criterion under compression and shear was considered to solve the problem of meso-simulation of concrete compression-shear cracking.The numerical simulation results verify the validity and correctness of the experimental results.It can be seen that the numerical simulation of this kind of problems not only has high scientific research significance,but also has high practicability.3)Simulate the cracking process of reinforced concrete simple-supported beams at macro level.In order to make the numerical simulation of crack morphology coincide with the actual cracking process of simple-supported beams,arbitrary-shaped aggregate is generated based on random aggregate delivery technology,and then the aggregate and other elements are meshed to realize the discrete mesh,so as to avoid the problem of non-convergence caused by the sensitivity of meshing.? At the same time,the Mohr-Coulomb damage constitutive program developed by the team is used as the damage constitutive model of simply supported concrete beams.This method takes into account the interaction of normal stress and shear stress of simply supported concrete beams under load,so that the simulation results are more accurate.