This study proposes an improved dual shear unified strength model by introducing the plastic internal variable which reflects the collective effects of strain softening, intermediate principal stress and unequal strength under tension and compression. The improved model is then simplified into simple forms for typical stress states, including uniaxial tension and compression, plane stress pure shear and tri-axial stress states. The smooth method and conjugate gradient method are utilized to facilitate its numerical implementation, avoiding numerical singularity and non-convergence in the solution process. The physical meanings of the parameters are further clarified and their values for self-compacting concrete are determined from the results of triaxial compression tests through a combination of direct determination, equation solution and back propagation (BP) neural network optimization. Validated against the test results, the improved model gives a more accurate prediction than the traditional dual shear unified strength model and Mohr-Coulomb model, in terms of both the overall trend and representative values. Validation results show that the improved model is applicable to materials for which the compressive strength is greater than the tensile strength and the tensile strength is greater than the shear strength.

中文翻译：

---

考虑应变软化效应的改进双剪切统一强度模型（IDSUSM）


本研究提出了一种改进的双剪统一强度模型，引入塑性内变量，反映应变软化、中间主应力和拉压下强度不等的共同影响。然后将改进的模型简化为典型应力状态的简单形式，包括单轴拉伸和压缩、平面应力纯剪切和三轴应力状态。利用平滑法和共轭梯度法方便其数值实现，避免了求解过程中的数值奇异性和不收敛性。进一步明确了参数的物理意义，并通过直接测定、方程求解和反向传播（BP）神经网络优化相结合的方式，根据三轴压缩试验的结果确定了自密实混凝土的参数值。经试验结果验证，改进模型无论是总体趋势还是代表值，都比传统双剪统一强度模型和Mohr-Coulomb模型的预测更加准确。验证结果表明，改进模型适用于抗压强度大于抗拉强度、抗拉强度大于剪切强度的材料。