Experimental Study of Plain Concrete under Triaxial Stress (original) (raw)
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The upcoming need of concrete structures designed against impulsive and extreme load due to natural hazards, industrial accidents or terrorists attack requires analytical modeling capable of reproducing material behavior in this range of loading. When a concrete structure is submitted to an impact or an explosion loading, material may be submitted to high triaxial compression stresses as well as tensile stresses due to reflection of compressive waves on free surfaces. Furthermore, the water saturation degree in massive concrete structures may be nearly 100% at core whereas the material is dry on the skin. Thus, the impact response of a massive concrete wall may depend on the water saturation state in the material. This paper first presents some triaxial tests performed at a maximum confining pressure of 100 MPa on a concrete representative of a containment building of a nuclear power plant. Experimental results show the constitutive behavior and its dependence to the water saturation ratio of concrete specimens. The second part of this study aims at modeling these tests by means of the coupled PRM constitutive model. Although its robustness and effectiveness, this constitutive model did not allow to accurately reproduce the response of concrete specimens observed during the tests. The differences between experimental and numerical results can be explained by both the influence of the saturation state of concrete and the effect of deviatoric stresses which are not well taken into account into the PRM model. Some modifications of the PRM model were carried out; they allow improving the numerical prediction of concrete behavior under high triaxial stresses and various saturation states.
The Influence of the Initial Concrete Strength on its Deformation under Triaxial Compression
The results of the experimental research of the influence of the initial strength of С20/25, С30/40, С40/50, С70/85 concrete classes on the principles of linear, volumetric and shear strains development in the conditions of triaxial compression are introduced in this article. Experimental research techniques and realized loading programs are described. The program of the triaxial uniform hydrostatic compression in the conditions of 1 = 2 = 3 < 0 has been realized during the first stage of the experiment. The testing has resulted in defining the relation “mean stress 0 –relative volumetric strain change ” for relatively high levels of loading. The values of additional plastic strains of the relative volume change pl characterizing deviations of experimental strain values from their design values according to the law of the elastic volume change el have been defined. However, higher values of pl correspond to lower strength concretes. The programs of non-uniform loading of the stress deviator at a mean stress invariable value (0 = const) have been realized during the second stage of the test. Experimental concrete specimens stress-strain curves in the directions of coordinate axes, diagrams of deviatoric stress and strain tensor components connection “i – i” as well as quantitative characteristics of the orthotropic concrete deformation process have been obtained. The determining influence of shear strains on dilatation effects in the concrete structure has been confirmed.
Damage of concrete in a very high stress state: experimental investigation
Materials and Structures, 2010
This study is intended to characterize the evolution in triaxial behavior of a standard concrete subjected to confining pressures varying from 0 to 600 MPa. Hydrostatic and triaxial tests, with several unloading-reloading cycles, are carried out on concrete samples using a high-capacity triaxial press. These tests serve to identify the evolution of the elastic unloading characteristics of concrete, depending on both confining pressure and axial strain. A number of optical observations are also provided to allow visualizing the evolution in concrete damage mode in the middle of the sample. Experimental results indicate a sizable change in concrete behavior with confining pressure. At low pressure values, Young's modulus decreases and Poisson's ratio rises sharply with axial strain. The concrete exhibits brittle behavior with failure caused by a localized damage mechanism. In contrast, at high confining pressures, the concrete becomes a ductile material, and the evolution in its unloading characteristics is negligible. Failure is thus associated with diffuse material damage. The concrete behaves like a granular material controlled by plasticity, meaning that the damage phenomenon observed at low confinement is completely inhibited.
Damage constitutive for high strength concrete in triaxial cyclic compression
International Journal of Solids and Structures, 2002
A constitutive relationship for high strength concrete in triaxial monotonic and cyclic compressions is developed based on the continuum damage mechanics. The bounding surface concept is employed in the formulation of the theoretical model. An experimental program was undertaken in order to establish databases for high strength concrete under triaxial monotonic and cyclic compressions. The stress-strain responses of high strength concrete subjected to triaxial monotonic and cyclic compressions were acquired through an experimental program. Comparison of the stress strain results indicates good agreement between the theoretical model and the experimental data. Ó
Strength and damage of concrete under high triaxial loading
European Journal of Environmental and Civil Engineering, 2010
This study focuses on identifying concrete behavior under severe loading (near field detonation or ballistic impacts). In order to reproduce high stress levels with well-controlled loading paths, static tests are carried out on concrete samples by mean of a very high-capacity triaxial press. Experimental results indicate a sizeable change in concrete behavior with confining pressure. At low pressure values, the concrete exhibits brittle behavior with failure caused by a localized damage mechanism. In contrast, at high ...
Concrete behavior under very high stresses
This communication concerns the concrete behavior under extreme loading situations (near field detonation or ballistic impacts). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. The validation of concrete behavior models, which simultaneously take into account the phenomena of brittle damage and irreversible strain such as compaction, thus requires test results that enable reproducing complex loading paths. Since 2004, the University of Grenoble has launched in collaboration with the French Ministry of Defense (DGA, Centre d'Etudes de Gramat) a research program on the vulnerability of concrete infrastructures. This presentation is devoted to the results of this program. Triaxial tests on a low-strength plain concrete have been performed, using a large capacity triaxial press named "GIGA". Stress levels overpassing one GigaPascal with homogeneous, static and well controlled loading paths have been reached. The results show that contrary to what is observed in simple compression, when placed under high confinement, concrete behaves like a granular stacking. There is not any influence of the level of the cement matrix strength whereas the saturation ratio exerts a major influence. The concrete strength capacity can be divided by 5 if the concrete is saturated instead of dried.
Cement and Concrete Research, 2008
The aim of this study is to characterize the behaviour of concrete under high triaxial loading at levels of confinement and axial stress of the order of the GigaPascal. This study is carried out within a more general scope of understanding concrete behaviour under impact. The studied concrete has properties as close as possible to those used in current construction projects. A triaxial press of high capacity is used to characterize the triaxial behaviour of concrete according to various loading paths. Hydrostatic, triaxial, proportional and oedometric tests are performed and show the influence of the loading path on the compaction process. The triaxial and proportional tests show the existence of strain limit states, defining a limit states threshold independent from the loading path.
Stress-strain behavior of plastic concrete using monotonic triaxial compression tests
Journal of Central South University, 2012
The mechanical behavior of plastic concrete used in the cut-off walls of earth dams has been studied. Triaxial compression tests on the specimens in various ages and mix designs under different confining pressures have been done and the stress−strain behavior of such materials and their strength parameter changes have been experimentally investigated. It has been observed that increasing the confining pressures applied on the specimens causes the material behavior to be alike the more ductile materials and the compressive strength increases considerably as well. Moreover, a parametric study has been carried out to investigate the influence of essential parameters on the shear strength parameters of these materials. According to the research, increasing the coarse to fine aggregates ratio leads to the increase of compressive strength of the specimens as well as the increase of the cohesion and internal friction angle of the materials. Furthermore, the bentonite content decrease and the cement factor increase result in an increase of the cohesion parameter of plastic concretes and decrease of the internal friction angle of such materials.
Dynamic properties of concrete materials with high rates of tri-axial compressive loads
Sustainability, 2000
This study is to find the dynamic properties of concrete materials under both high strain-rates and triaxial stress states and to formulate the dynamic constitutive model of concrete. Thus, triaxial rapid compressive loading tests for concrete specimens were executed. In tests, the compressive strength of concrete, the confining pressure and the loading rates were chosen as test parameters. Based on test results, the influence of these parameters on the mechanical properties of concrete are examined, and then the constitutive model of concrete with the strain-rate effects is proposed.
DYMAT 2009 - 9th International Conferences on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2009
This paper concerns the concrete behavior under extreme loading situations (ballistic impacts, penetration). During such loadings, concrete material is subjected to very high-intensity triaxial stress states. For the purpose of reproducing such stress levels with well-controlled loading paths, static tests have been conducted on concrete samples using a triaxial press offering very high capacities (stress levels of around 1 GPa). This paper is devoted to experimental results which show that the concrete strength in uniaxial compression after 28 days of ageing, f c28 , is a very poor indicator of the high-pressure mechanical response of concrete. From the composition of a reference ordinary concrete (f c28 = 29 MPa), two other concretes have been produced with f c28 equal to 21 MPa and 57 MPa, respectively. Besides, to evaluate the effect of the saturation ratio, Sr, tests have been conducted on both dried samples, wet samples and saturated samples. The results show that contrary to what is observed in simple compression, when placed under high confinement, concrete behaves like a granular stacking. There is no more effect of the cement matrix strength whereas the concrete saturation ratio exerts a major influence.