Experimental Study And Theoretical Analysis On Multiaxial Dynamic Performance Of Concrete

Concrete is widely used in the field of engineering construction because of its unique advantages.With the rapid development of engineering technology and the continuous change of engineering requirements,high-rise structures,long-span bridges and other special engineering structures can appear and put forward new requirements.In these special structures such as high-rise and long-span bridges,the influence of structural self weight has brought about further development of this type of engineering It must be bothering.Lightweight aggregate concrete has the characteristics of light weight,high strength,good thermal insulation and fire resistance,which can effectively reduce the self weight of concrete structure.It has been widely concerned by scholars at home and abroad and applied in engineering field.The application of concrete in the actual structure is not only affected by the uniaxial stress state,but also by the multiaxial stress state.The research on the multiaxial mechanical properties of concrete is helpful to further understand the mechanical properties of concrete.At the same time,in practical engineering,concrete is not limited to static load,but also subjected to dynamic actions such as earthquake,wind and impact explosion.Concrete has obvious rate effect.It is of great significance to study the mechanical properties of concrete by considering the actual stress state of concrete structure and the dynamic action.In this paper,four loading strain rates(10^-5/s,10^-4/s,10^-3/s and 10^-2/s)and seven multi axial loading modes（uniaxial compression,uniaxial tension,pure shear,biaxial compression compression,biaxial tension compression,triaxial compression compression and compression shear）are considered to study the mechanical properties of ordinary concrete and lightweight aggregate concrete,and the multiaxial dynamic characteristics of ordinary concrete and lightweight aggregate concrete are compared and analyzed According to the experimental results,the multiaxial dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete are proposed.At the same time,the multiaxial dynamic constitutive relation of ordinary concrete and lightweight aggregate concrete is put forward based on the theory of elastic-plastic damage.The concrete specimens and the concrete structural members in the literature are analyzed by using finite element through the secondary development of UMAT subroutine,and compared with the test results to verify the multiaxial dynamic constitutive relation of ordinary concrete and lightweight aggregate concrete proposed in this paper The applicability of.The main research contents are as follows:（1）Based on the analysis of the influence of rotation effect,bending effect and friction effect of the current concrete shear multiaxial test technology on the test results,the design of reasonable test technology and the way of specimen size to control the adverse impact on the shear multiaxial test results,through the shear test to verify that the concrete shear test technology in this paper can meet the test measurement requirements.（2）Through the test and analysis of uniaxial loading dynamic performance of ordinary concrete and lightweight aggregate concrete,the strength values of uniaxial compression,pure shear and uniaxial tensile loading mode increase gradually with the increase of strain rate,among which the strength of tensile loading mode increases the most,the strength of pure shear loading mode increases the next,and the strength of compression loading mode increases the least;the strength of ordinary concrete single shear loading mode increases the least The influence of the loading strain rate on the axial strength is lower than that of the lightweight aggregate concrete,and the relationship between the uniaxial strength improvement coefficient and the dimensionless value of the loading strain rate is linear.（3）According to the biaxial compression test and biaxial tension compression test of ordinary concrete and lightweight aggregate concrete,under the same lateral compression stress,with the increase of loading strain rate,the biaxial compression stress and biaxial tension compression stress of ordinary concrete and lightweight aggregate concrete increase gradually,and the influence of loading strain rate on the principal stress of lightweight aggregate concrete is higher than that of ordinary concrete Under the same loading strain rate,the biaxial compressive stress of ordinary concrete and lightweight aggregate concrete is higher than the uniaxial compressive stress under the action of lateral compressive stress.With the increase of lateral compressive stress,the biaxial tensile compressive stress of ordinary concrete and lightweight aggregate concrete decreases gradually,and the change degree of the principal stress of ordinary concrete affected by the lateral compressive stress is higher than that of lightweight aggregate concrete High.The main stress of biaxial compression with lateral compressive stress is less affected by the loading strain rate than that without lateral compressive stress,and the biaxial tension compression loading mode is the opposite.At the same time,based on Kupfer biaxial criterion and Japanese dam code,the biaxial compression and biaxial tension compression dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete are put forward.（4）Through the triaxial compression compression test of ordinary concrete and lightweight aggregate concrete,the same lateral compressive stress increases with the increase of loading strain rate,the main compressive stress of ordinary concrete and lightweight aggregate concrete increases gradually,and the effect of loading strain rate on the main compressive stress of lightweight aggregate concrete is higher than that of ordinary concrete.With the same loading strain rate,the main compressive stress of ordinary concrete and lightweight aggregate concrete increases obviously with the increase of the lateral minimum pressure stress.When the lateral minimum pressure stress is the same,the main compressive stress of ordinary concrete and lightweight aggregate concrete is not obviously affected by the lateral maximum pressure stress,and the main compressive stress of ordinary concrete is higher than that of lightweight aggregate concrete.When the lateral lowest pressure stress increases,the influence range of triaxial compressive stress of ordinary concrete and lightweight aggregate concrete decreases gradually.At the same time,through the secondary uniaxial loading,the residual mechanical properties of ordinary concrete and lightweight aggregate concrete gradually decrease with the increase of the lateral minimum stress,and the ratio of residual strength of lightweight aggregate concrete is lower than that of ordinary concrete.（5）Through the compression shear multiaxial test of ordinary concrete and lightweight aggregate concrete,the shear stress of ordinary concrete and lightweight aggregate concrete increases with the increase of loading strain rate.When the lateral compression stress is large,the influence of loading strain rate on the shear stress of two kinds of concrete decreases,and the shear stress of lightweight aggregate concrete is affected by loading strain rate The effect is higher than that of ordinary concrete.With the increase of lateral compressive stress,the shear stress of ordinary concrete and lightweight aggregate concrete increases with the same loading strain rate.When the lateral compressive stress is large,the increase of lateral compressive stress makes the increase range of shear stress of the two kinds of concrete decrease.The shear stress of ordinary concrete is higher than that of lightweight aggregate concrete.When the lateral compressive stress is large,the shear stress of ordinary concrete and lightweight aggregate concrete is gradually reduced under the influence of loading strain rate.At the same time,according to the compressive shear stress space and plane principal stress space,the dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete are put forward.（6）According to the strain rate effect and different multi axial loading methods,this paper puts forward the corresponding stress mechanism model,and analyzes the stress mechanism of concrete in this paper.The multi axial loading mode improves the plastic deformation ability of ordinary concrete and lightweight aggregate concrete,and the effect of strain rate on the deformation parameters of ordinary concrete and lightweight aggregate concrete is more discrete.Based on the test data of ordinary concrete and lightweight aggregate concrete under multiaxial dynamic loading in this paper,the multiaxial dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete are proposed by optimizing Ottosen failure criterion,and based on the double shear strength theory,two kinds of dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete with different loading strain rate effects are proposed.（7）Based on the optimal Ottosen failure criterion,the dynamic failure criterion equations of ordinary concrete and lightweight aggregate concrete are obtained and the corresponding yield criterion equations are calculated.The multiaxial dynamic constitutive relation of ordinary concrete and lightweight aggregate concrete is put forward by the elastic-plastic damage theory.It is developed by the UMAT subroutine and applied to the finite element calculation.It is compared with the test results and the concrete in the literature The results are compared and the corresponding dynamic expansion calculation is made to verify the applicability of the constitutive relationship proposed in this paper.