| Concrete structure are subjected to multiaxial quasi-static load as well as dynamic loads such as wind load、earthquake load、impact load and so on. In existing research results on multiaxial dynamic performance of concrete, the studies of impact load are much more than earthquake load. Therefore, it is of great importance to study the multiaxial behavior of concrete under earthquake load.Steel Fiber Reinforced Concrete(SFRC)is a new kind of engineering composite. Because of excellent physical and mechanical performance including high ductility、high toughness and anti-blasting ability and so on. It has been widely used in highway、safeguard structure and airport runway, etc. While the studies of properties of SFRC under quasi-static load and impact load are much more than multiaxial behavior of SFRC under seismic load. The kind and volume content of steel fiber and so on also have great influence on the physical and mechanical properties of SFRC. It is of great theoretical significance and practical value to complete multiaxial dynamic experimental study of concrete with different steel fiber volume contents under various strain rates and stress ratios and establish a multiaxial dynamic strength critieria of SFRC for the seismic design of and concrete structure and dynamic nonlinear analysis of concrete structure.A series of concrete biaxial dynamic tests are carried out by the triaxial static and dynamic testing machine designed at Dalian University of Technology, China. The steel fiber volume contents were 0%,1%,2%,3%, the stress ratios were 1:0,1:0.25,1:0.5,1:0.75,1:1, the strain rates were 10-5/s, 10-4/s,10-3/s,10-2/s. The article studies stress-strain relationship, strength properties、deformation characteristics and failure criteria of concrete with different steel fiber volume contents under various stress ratios and strain rates. A octahedral stress space failure criteria was established. Detail research contents and conclusions are presented as follows:(1) Based on the Ottosen criterion, by the analysis of multiaxial static and dynamic strength test data of numerous concrete specimens, which are classified into different strength grades, a multiaxial dynamic strength criterion is reasonably established, in which both the strain rate effect and the strength of concrete are taken into account. It is proved that the predicted strength of the failure criterion is in good agreement with the basic requirements of continuity, smoothness and convexity and reflecting the change rule of dynamic strength. (2) Uniaxial compression dynamic tests for SFRC under strain rates of 10-5/s～10-2/s are carried out. Dynamic strength properties, deformation characteristics, specimen failure modes of concrete with different contents of steel fibers under various strain rates are studied. The influence of steel fiber volume content and strain rate on the strength increase factor is analyzed. The compressive strength of concrete increase with the increase of strain rates and the increase factor of concrete with 3%volume contents obtain the maximum value.(3) Stress-strain curves and failure modes of concrete under biaxial compression are obtained. The tests investigate the influence of stress ratio, strain rate and volume content of steel fibers on the mechanical properties of concrete such as ultimate strength, elastic modulus, deformation characteristic, stress-strain curve and the compressive toughness index. The compressive strength of concrete increase with the increase of strain rates and firstly increase and then decrease with the increase of stress ratio; when the strain rate increase, the compressive toughness index of plain concrete increase while the compressive toughness index of concrete with 2%and 3%steel fiber volume contents and the enhanced ability of steel fiber on concrete decrease.(4) Based on test results, a biaxial dynamic failure criterion of SFRC taking stress ratio, strain rate and steel fiber volume content into consideration is established. |
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