基于多龄期弹塑性损伤徐变模型的大坝混凝土应力状态评价

It is evitable to undergo partial damage creep for concrete dam under large load. Elastic creep model is the widespread used method for dam concrete creep stress simulation analysis at present. However, although it considers concrete age of loading and loading time, the plastic flow or release of high stress cannot be well reflected, which may lead to inconsistence of calculated results and the actual one, even mistake the risks of concrete cracking and plastic damage under some circumstance. A new model is established in this study. Firstly, concrete creep test of multi-age and high stress is carried out by applying fiber Bragg grating sensor to obtain high accuracy creep test curve. Secondly, multi-aged elastic-plastic damage creep model is built by integrating viscoelastic plasticity unified constitutive theory and Koiter hypothesis, and constitutive integral arithmetic for the new model is designed. Then, parameters of the new model are deduced based on the principle of parameter decoupling and step-reversion. Finally, the change law of the ratio of concrete elasticity modulus and viscosity coefficient as contract aging is dug to obtain the relation of flow coefficient in viscoplasticity model and concrete age. The new model is of great significance for improving the stress analysis accuracy and crack width prediction of concrete dam as well as acknowledgement of creep property under high stress.

混凝土大坝在较大的荷载作用下，局部出现损伤徐变在所难免。目前大坝混凝土徐变应力仿真分析所采用的弹性徐变模型，尽管考虑了混凝土加载龄期和持荷时间，但不能反映高应力的塑性流动或释放，导致计算的应力与实际不符，在一些情况下会错误地评价混凝土开裂或塑性损伤的危险性。本项研究采用光纤Bragg光栅传感器进行多龄期、高应力比下的混凝土徐变试验，获得高精度徐变试验曲线；然后融合黏弹塑性统一本构理论以及Koiter假定，建立多龄期下的弹塑性损伤徐变模型，设计新模型本构积分算法；接着基于参数解耦、逐步反演的原则，推演新模型的参数；挖掘混凝土弹性模量和粘滞系数的比值随着混凝土龄期的变化规律，建立黏塑性模型中流动系数与混凝土龄期的关系。新模型对提高混凝土大坝应力分析精度、裂缝宽度的预测和高应力下混凝土徐变特性的认识具有重要的意义。

混凝土大坝在较大的荷载作用下，局部出现塑性徐变在所难免。目前大坝混凝土徐变应力仿真分析所采用的弹性徐变模型，尽管考虑了混凝土加载龄期和持荷时间，但不能反映高应力的塑性流动或释放，导致计算的应力与实际不符，在一些情况下会错误地评价混凝土开裂或塑性损伤的危险性。.本项研究在室内试验方面，针对水胶比为0.5，砂率为0.3，粉煤灰掺量为0.35的C30二级配混凝土，开展了多龄期、不同应力比下的混凝土徐变试验，获得了一系列精度良好的混凝土徐变曲线；在徐变模型建立方面，基于岩石流变学中广义Kelvin模型、西原模型和七元件非线性黏弹塑模型等黏弹塑性流变模型，分别建立了多龄期稳态徐变模型、亚稳态徐变模型及破坏型徐变模型；在本构积分算法方面，设计并推导了多龄期的弹塑性徐变温度应力仿真分析的隐式和显式本构积分算法；采用应力增量法和叠加原理, 设计并推导了变应力作用下的拉压异性徐变的弹性徐变问题的有限元算法；与此同时，设计并推导了考虑塑性徐变的三维空间实测应变转换应力的算法，以及探讨了考虑拉伸压缩异性徐变的实测应变转换应力算法；此外，在徐变模型参数反馈方面，探讨并给出了一套基于三维空间应变计组实测应变的大坝混凝土实际徐变度的反演方法；结合实际混凝土工程，初步展示了建立的新模型和新算法。新模型对提高混凝土大坝应力分析精度、合理评价大坝混凝土应力状态具有重要的意义。