The Research On The Size Effect Of Concrete Behavior In Biaxial Compression

The mechanical properties of concrete is closely related to the specimen size, systematic study of concrete specimen size effect is needed, to accurately describe different concrete mechanics performance. Scholars at home and abroad studied force and deformation properties of the size effect about concrete material under uniaxial loading, carried out experimental researches and made theoretical analysis. In the actual stress state, the concrete structure is under the complex stress state with coupled action of multidimensional load rather than the simple uniaxial compression or tension. However, the literature about multiaxial stress performance in the study of concrete size effect was rarely reported, and related research is still inadequate. Restricted by various factors,the size effect of the experimental study is often limited within a smaller scale. Adopting the method of numerical simulation can effectively recover the deficiency of test research, which provides another mean to the study of the size effect.Based on the discussion above, this paper systematically studies biaxial compression performance of concrete size effect with the methods of experimental study and numerical analysis. The main research content is as follows:(1)The cube specimens of 100 mm, 150 mm and 200 mm length were used to the biaxial compression experiment research, with the lateral loading rate of 0, 0.1,0.2, 0.25, 0.3,0.4, 0.5. The results show that the strength, peak strain and ultimate strain of concrete biaxial compression have obvious size effect phenomena. When the biaxial compressive strength of concrete under loading ratio from 0.1 to 0.5, size effect phenomena weaken with the increase of load ratio. Peak strain and ultimate strain of size effect weaken on the lateral load ratio from 0 to 0.3, but it strengthens on the lateral load ratio from 0.3 to 0.5. When peak strain on lateral loading rate of 0.3, the size effect is most unconspicuous. The biaxial compressive strength of each cube concrete specimen decreases with increasing specimen geometry size.The biaxial compressive strength of same size improved with the lateral load ratio increased. With the increase of specimen geometry size, peak strain and ultimate strain increase accordingly. Different sizes of the concrete specimens on the loading ratio of 0.25,peak strains and ultimate strains reach maximum value. The size effect of concrete biaxial compressive secant modulus is very small, which can be neglected in the analysis and calculation.(2)Base on systematic analysis of statistical theory of size effect and the experimental data, the values of the parameters in the formula of the law of statistics size effect aboutconcrete biaxial compression cube compressive strength can be determined. Critical size and critical strength of concrete biaxial compression on each loading ratio is also analyzed.(3)By establishing the analysis model of random aggregate of concrete, the mechanical properties parameters of the bonding interface layer is obtained. The homogeneous elastic brittle mechanics model is used to simulate concrete cube biaxial compression process. By fitting the results to numerical concrete biaxial compressive strength, and the formula of size effect law about numerical biaxial compressive strength of concrete cube is deduced.