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.

在长期负荷作用下，混凝土材料的蠕变变形对水工结构的安全性产生严重影响，尤其是在超高压水平的作用下，混凝土材料将经历非线性蠕变，极易引发结构损坏。本研究通过混凝土试样的单轴非线性蠕变试验，基于超声波探伤的波速值建立损伤指数，并获得了混凝土试样的蠕变与损伤程度曲线。将理想的弹性元件、Kelvin体以及非线性粘弹塑性元件串联，提出了考虑混凝土蠕变特性的新型粘弹塑性模型。基于最小二乘原理，运用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进行模型验证。同时，分析了各个模型参数的敏感性。研究表明，LM算法能够更佳、更快地给出模型的拟合参数，且模型的拟合值与实验结果相似。参数敏感性分析表明，所提模型具有良好的稳定性和适应性。该模型对蠕变各阶段的描述更为精确，便于在实际情况中的混凝土蠕变计算应用。