| This article proposes a new double yield surface constitutive model based on Sub-loading surface theory, one of the yield surfaces is a volume yield surface and the other is a shear yield surface. This model adapts to a variety of complex stress path loading and it uses the equivalent plastic strain as an internal variable to describe the stress-strain behavior of concrete under cyclic loading. Before loading, the Sub-loading surface and the normal yield surface is a point in principal stress space. When loading, with the accumulation of plastic strain, the normal yield surface extends through the form of equivalent hardening; but the extended form of the Sub-loading surface is a mixed hardening form. When the Sub-loading surface and the normal yield surface coincide, the Sub-loading surface will reach to the failure surface as the extended form of normal yield surface. At the process of stress-strain curves into the decline, there is only the shear yield surface to make an effect. Because following the strain continues to increase, but the stress gradually reduces, so the stress point no longer reaches to the volume yield surface, and the volume yield surface does not make an effect.The model is intended to simulate the constitutive behavior of concrete under complex stress state. Application of the Fortran language computer program, this article simulates seven loading modes which are the proportion of cyclic loading, respectively1:0.1:0.1,1:0.15:0.15,1:0.2:0.2, and fixed lateral pressure values, respectively lOMPa、20MPa、30MPa、40MPa、Compared with the experimental curves and model curves we can know, there is a certain error of the curves before the peak, but the biggest error is within the range of20%; And after the peak, there is a big error, but the trend is consistent with the experimental law; And at this range the simulated curves perform the phenomenon of expansion. Therefore, the model can simulate the constitutive behavior of concrete materials under cyclic loading. |
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