循环荷载作用下水在混凝土中的动态输运及其对混凝土破坏的影响机理

Engineering examination evidenced that the damage of concrete structure developed more quickly and the failure mode was changed significantly under the coupling effect of free water and cyclic loading. However, the related investigations on this issue, such as the prediction model of concrete fatigue properties under the impact of free water, the water dynamic migration process in fatigue damaged concrete, and the formation mechanism of hydrodynamic pressure in concrete, are not found at present studies. As a result, the performance and the service life of free water incorporated concrete can not be accurately predicted. Therefore, the aim of this project is to solve the problems mentioned above. The research objects include the free water in the concrete pores and cracks, and the cracked and intact concrete. To detect the hydrodynamic pressure in concrete caused by free water, a new test method will be developed. To track the fatigue damage, some advanced techniques will be adopted. Moreover, the experimental, theoretical and numerical investigation methods will be systematically combined to figure out the following issues: the migration of free water in damaged concrete, the pressure formation mechanism and the action model of free water in the concrete, the damage evolution of water incorporated concrete, the failure mechanism of water incorporated concrete, the evaluation methods and the prediction model on the performance of concrete under the coupling effect of free water and cyclic loading. The research results can be expected to provide scientific references for structural design, performance assessment, life prediction, and strategy decision on the concrete structures in the water environment.

工程调查表明水-循环荷载耦合作用下混凝土的病害发展迅速、破坏状态明显变化，然而无论是水-循环荷载耦合作用下的混凝土疲劳性能预测，还是水在疲劳损伤混凝土中的动态运移，或者是混凝土内动水压力的形成及作用机理，目前都罕有研究涉及，制约了水-循环荷载耦合作用下混凝土结构的全寿命设计、混凝土结构性能与寿命的正确评价。因此，本项目采用先进的测试分析技术，克服混凝土内动水压力难以测试、混凝土损伤动态演化难以追踪的难题，以孔隙/环境中的自由水、开裂/完好混凝土为研究对象，开展试验研究、理论分析和数值模拟，探索不同工况下混凝土中水的动态运移规律、动水压力的形成机制及作用模式、混凝土疲劳特征参量的衰变规律，在科学揭示自由水对混凝土疲劳性能影响规律及对损伤演化影响机理的基础上，建立水-循环荷载耦合作用下混凝土破坏分析方法，为含水混凝土工程设计、性能评价、寿命预测以及减损策略制定提供科学依据。

混凝土结构经常在有水的环境中工作，环境中的自由水会渗入混凝土内部形成不同湿度的混凝土。混凝土在含水环境中工作时又会受到疲劳等各种动力荷载的作用，水与循环等动态荷载的耦合作用，会导致结构性能与破坏形态发展较大的变化。工程调查结果也表明水-循环荷载耦合作用下湿态混凝土的病害发展迅速、破坏状态明显变化。然而水-循环荷载耦合作用下的混凝土疲劳性能预测，已有研究以及标准规范中罕有涉及，制约了水-循环荷载耦合作用下混凝土结构的设计、结构性能与寿命正确评价。.本项目通过试验研究、理论分析与数值模拟相结合的手段，明确了水对混凝土静动力力学性能的影响规律，揭示了动荷载下混凝土强度变化机理，研究了孔隙及裂缝中的水对混凝土疲劳特性的影响规律、水压力在裂缝中的空间分布规律，探索了循环荷载作用下水对混凝土裂缝扩展的影响机制，对混凝土的疲劳损伤与疲劳寿命进行了预测分析。研究结果表明：干燥混凝土的疲劳强度高于规范值，而饱和以及水环境中工作的混凝土的疲劳强度远低于规范值，混凝土受到水的渗入会造成疲劳性能的下降，会导致不满足规范要求而产生一定的安全隐患。因此，对长期在水中工作的结构混凝土，计算其疲劳强度时一定要考虑水分的影响。本项目相关研究成果可为涉水混凝土结构的全寿命设计、损伤诊断与寿命评估提供科学依据。