Experimental Study On The Multi-axial Dynamic Behavior Of Plain Concrete

Concrete is a widely used construction material in modern architectures. Dynamic load (such as earthquake load, impact load, explosion load, vehicle load, waves load, wind load, etc.) can cause the damage and collapse of buildings, which can lead to casualties and property losses. In structure design, it is a difficult point to the analyses of complex dynamic force, such as the force analyses of beam-column connections, nuclear containments and concrete arch dams. Since China lies in the earthquake belt along the west of the Pacific Ocean, She is a multi-earthquake-happening country. In existing research results, the works of uniaxial dynamic behavior are much more than these of multi-axial dynamic behavior, the works of concrete dynamic behavior under explosion load and impact load are much more than these of earthquake load. Therefore, it is very important to study the dynamic behavior of concrete under multi-axial stress.A series of concrete multi-axial dynamic tests are carried out by the triaxial static and dynamic testing machine. The tests include several stress states:uniaxial compression, uniaxial tension, biaxial compression with constant lateral pressure, biaxial proportional compression, triaxial compression, biaxial tension-compression. The strain rates were10-5s-1,10-4s-1,10-3s-1and10-2s-1. In the UMAT of ABAQUS, the program of concrete endochronic damage constitutive model is written. The corresponding numerical models are established, and the numerical calculations are carried out.The main research contents are as follows:1Uniaxial compression and uniaxial tension dynamic tests are carried out. Specimen failure modes, dynamic strength, peak strain and the secant modulus at peak load are obtained. The relationships between the uniaxial strength and strain rates are obtained. Stress-strain curves are obtained.2The tests of biaxial compression with constant lateral pressure and biaxial proportional compression are carried out. Specimen failure modes, biaxial compressive dynamic strength, vertical peak strain are obtained. Lateral peak strain and the poisson ratio are obtained, which are caused by vertical load. The influence of loading paths on biaxial compressive strength is discussed, and the loading paths include biaxial proportional compression and biaxial compression with constant lateral pressure. Under biaxial compression, the mechanism of strength increase is discussed. From lateral deformation, the reason of biaxial compressive strength changing with middle principal stress is explained. The dynamic failure criteria are respectively established.3The tests of triaxial comprssion are carried out. The specimen failure modes, the triaxial compressive dynamic strength, the vertical and lateral peak strain are obtained. The formulas of triaxial dynamic strength are obtained. The strengths of monotonic loading and cyclic loading in vertical direction are compared. Under triaxial compressive dynamic loading, energy dissipation of concrete and damage of concrete are researched.4The tests of concrete biaxial dynamic tension-compression are carried out. Specimen failure mode, the tensile-compressive dynamic strength, the peak tensile strain and the peak compressive strain are obtained. The changing rules of strength or strain with strain rates and lateral tensile stress are obtained. The dynamic criterion under tension-compression is established.5Using the testing data of this paper, in octahedral space, the multi-axial dynamic criterion is established, in which the range of strain rates is10-5s-1-10-2s-1. For the usability of engineering, three groups of parameters of tensile meridian and compressive meridian are given, which respectively are upper limit, average and lower limit.6Based the multi-axial dynamic failure criterion and endochronic damage constitutive model, using UMAT of ABAQUS, the numerical computations are carried out, and the results prove that the material model is agreeing with the testing results of this paper.