Study On The Dynamic Behavior Of Saturated Large Aggregate Concrete Under Biaxial Loading With Tests

Concrete structures are often erected in the ambient water.The mechanical properties of the concrete will be affected by the ambient water pressure,pore water pressure.Therefore,the design strength and the serviceable life of the concrete structures in the ambient water will be influenced.Large aggregate concrete is the common used materials of the mass concrete structure.Studying the mechanical properties of large aggregate concrete under the dynamic load of multiaxi is the basis of research and analysis of seismic performance for mass concrete structure,mass concrete structure is the basis of research and analysis of seismic performance,which has great significance to the design and durability for mass concrete structure under seismic action.Supported by the National Natural Science Foundation of China.(Project number:51079019).Based on triaxial static and dynamic test equipment,Both dry and saturated large aggregate concrete under uniaxial and biaxial stress state in dynamic performance were studied.The uniaxial dynamic properties of dry and saturated large aggregate concrete were researched experimentally.By the affected of strain rate about compressive and tensile strength,stress-strain curve,and peak strain of dry and saturated large aggregate concrete were analyzed.The failure mode is similar between the dry and saturated concretes under the same strain rate.The microcracks readily develop and grow along the aggregate-matrix interfaces due to high stress concentrations at these interfaces and due to weak interfacial bonding.The strength and elastic modulus of both kinds concretes increased with the increase of strain rate.More coarse aggregates are broken along the fracture surfaces with the increase of strain rate.Compared with the test results of dry concretes,the uniaxial compression and uniaxial tension strength of saturated concrete increased more than that of dry concrete.Because of the viscosity of free water and inertia effect,which leads to the enhancement of dynamic strength of saturated concrete.Based on the test result,the relationship of strain rate and strength and peak strain was established.The dynamic properties of dry and saturated large aggregate concrete under biaxial compression stress state were researched experimentally.The failure modes,strength,peak strain and stress-strain curve was affected by the strain rate and stress ratio.Under the condition of static loading,some uniform distribution cracks in the direction parallel to the loading,the number of cracks increased and more coarse aggregates are broken along the fracture surfaces with the increase of strain rate.The macroscopic failure pattern of specimens mainly determined by the stress ratio,and little influence on strain rate.The ultimate strength of both kinds concretes in biaxial compression state is higher than the uniaxial compressivestrength at any strain rate.The maximum biaxial strength occurs at a stress ratio of 0.5 for any strain rate investigated.The static compressive strengths of saturated concrete are lower than those of the dry concrete at all the stress ratios involved in the current study.On the contrary,however,the dynamic compressive strengths of saturated concrete are higher than those of the dry concrete under high strain rate.The failure of concrete is controlled by the development of cracks.Under the condition of quasi static loading,the volume deformation of concrete lies in compressive state before peak stress.Therefore,free water in the saturated concrete is pushed into the tip of cracks,which acts as a wedge to the crack.Under dynamic loading,such as that produced by near-field denotation or ballistic impacts on concrete infrastructure,can generate very highintensity triaxial stress states in concrete materia,because of the viscosity of free water and inertia effect,which leads to the enhancement of dynamic strength of saturated concrete.The dynamic failure criterion of both kinds concrete under biaxial compression were proposed in principal stress space and octahedral stress space.The dynamic properties of dry and saturated large aggregate concrete under biaxial tension-compression stress state were researched experimentally.The failure modes,strength and peak strain of dry and saturated large aggregate concrete were analyzed under the dynamic condition.The macroscopic failure modes of concrete specimens have little influence on moisture content.Both saturated and dry concrete specimens were ruptured by only one apparent tensile crack perpendicular to the direction of tensile load.The failure modes of dry and saturated large aggregate concrete specimens is the same as uniaxial tensile test.Damage cracks are mainly caused by the limit tensile strain.Lateral compressive stress will not affect the failure modes of concrete specimens.The strength of both kinds concrete under biaxial tension-compression increases with the increase of strain rate.The dynamic tensile strength of both concrete increases with the increasing strain rate,and reduce with the increasing lateral pressure.No strain rate effect on peak strain but great stress ratio effect on the peak strain.The normalized strength under biaxial tension-compression of dry concrete is higher than that of saturated concrete under the same confining pressure.Whereas,under dynamic loading,the saturated concrete has high strength.Under the condition of quasi static loading,the static tensile strength of wet concrete decreases due to free water in the cracks.Under the condition of dynamic loading,the viscous resistance of free water,well known in physics as Stefan effect,could give opposing stress at the tip of cracks at the same time.Which leads to the enhancement of dynamic strength of saturated concrete.The dynamic failure criterion of both kinds concrete under biaxial tension-compression were proposed in principal stress space and octahedral stress space.On the basis of the test in this paper,based on the theory of endochronic and damage mechanics,considing the factors of saturated water and aggregate gradation and the strain rate on mechanical properties of large aggregate concrete.The constitutive model is established.The calculation procedure is used to analyze the biaxial dynamic loading test.The calculation results are agree with test results which shows under the condition of saturated water factors,the model can well reflect the dynamic performance of the concrete in biaxial loading state.Finally,the application of the proposed constitutive model in the xiaowan arch dam about the nonlinear dynamic analysis.Calculation results conform to the law of the arch dam in saturated water environment which subject to dynamic loading.The tensile strength and strain of arch dam are increasing.The research results in this paper will provide reference for seismic safety evaluation of the construction structure in the water environment.