Nonlinear creep test data

Under long-term load, the creep deformation of concrete materials has a serious impact on the structural safety of hydraulic structures, especially under the action of ultra-high stress levels, the concrete materials will undergo nonlinear creep, which is extremely easy to cause structural damage. In this study, the uniaxial nonlinear creep test of concrete specimens was used to establish the damage index based on the wave velocity value of ultrasonic flaw detection, and the creep and damage degree curve of the concrete specimen were obtained. The ideal elastic element, the Kelvin body, and the nonlinear viscoplastic element are connected in series, and a new viscoelastic plastic model considering the creep characteristics of concrete is proposed. Based on the principle of least squares, the Levenberg-Marquardt (LM) algorithm is used to inverse the parameters of the nonlinear creep test. In addition, the model is verified by the measured data of linear creep. At the same time, the sensitivity of each model parameter is analyzed. The research shows that the LM algorithm can give the fitting parameters of the model better and faster, and the fitting values of the model are similar to the experimental results. The sensitivity analysis of the parameters shows that the proposed model has good stability and good adaptability. The model has a more accurate description of the various stages of creep, and may be conveniently applied to concrete creep calculations in actual projects.

在长期荷载作用下，混凝土材料的蠕变变形对水工结构的结构安全具有显著影响；尤其当处于超高应力水平作用时，混凝土材料会发生非线性蠕变，极易引发结构损伤。本研究通过开展混凝土试件的单轴非线性蠕变试验，基于超声探伤的波速值构建损伤指标，得到了混凝土试件的蠕变与损伤度曲线。将理想弹性元件、开尔文体与非线性黏塑性元件串联，提出了一种考虑混凝土蠕变特性的新型黏弹塑性模型。基于最小二乘原理，采用莱文贝格-马夸特（Levenberg-Marquardt, LM）算法对非线性蠕变试验的参数进行反演。此外，通过线性蠕变的实测数据对所提模型进行验证，并对各模型参数开展敏感性分析。研究结果表明：LM算法能够更优且更快地求解得到模型的拟合参数，模型拟合值与试验结果吻合度较高；参数敏感性分析显示，所提模型稳定性良好、适应性较强，可精准描述蠕变的各个阶段，且便于应用于实际工程中的混凝土蠕变计算。