Study On Size Effect Of Bending Performance Of Concrete Based On Cosserat Elastoplastic Theory

The size effect of concrete bending behavior can not be explained by classical continuum theory.Cosserat continuum theory is a more generalized continuum theory developed on the basis of classical continuum theory.It regards objects as micro-structures with continuous distribution and certain size,takes into account the rotation between micro-structures,and introduces the intrinsic size of materials as the internal scale parameter in the constitutive relationship.Thus,the relationship between macro scale and micro scale is established.Based on the virtual displacement principle,a concrete finite element numerical analysis model based on Cossserat elastic-plastic theory was established to simulate the concrete bending performance test.The numerical simulation results was compared with the existing experimental data to study the size effect of concrete bending performance.The main contents of this paper are as follows:(1)Firstly,through the numerical simulation of concrete bending tests of different kinds and sizes,it was verified that the Cosserat numerical solution considering the intrinsic size parameters was in good agreement with the existing experimental results,which shows that Cosserat elastoplastic theory makes up for the shortcomings of classical continuum theory and can explain the size effect phenomenon of concrete bending performance.Based on the yield criterion of maximum tensile stress,the four-point bending and three-point bending tests of concrete were numerically simulated and compared with the existing experimental data.Thus,the intrinsic size of five kinds of concrete were determined.(2)The factors affecting the intrinsic size of concrete were analyzed according to the composition of concrete.The influence of seven factors on the intrinsic size of concrete,such as concrete strength,water cement ratio,sand content,coarse aggregate strength,maximum aggregate size,gradation and age,were mainly studied.The results show that the intrinsic size of concrete increases with the increase of concrete strength.(3)The influence of dimension parameters on flexural strength and stiffness of concrete was studied.The results show that the bending strength increases with the increase of dimensionless ratio of intrinsic size to specimen height.That is to say,the bending strength of the material increases with the increase of intrinsic size at the meso level,and decreases with the increase of height and span at the macro level.The height of the specimen has a significant effect on the size effect of the bending strength,while the span has little effect on the size effect of the bending strength.(4)The finite element calculation model of concrete with notches was established.The size effect of flexural properties and fracture toughness of notched concrete was studied.The results show that the size effect of the notch on the flexural properties of concrete is weakened.