混凝土材料的动力性能是大坝结构动力安全评价需考虑的主要因素之一。由于大坝混凝土中存在大粒径骨料，动力试验必须采用大尺寸试件。但目前采用大尺寸混凝土试件进行冲击性能的研究较少，对于混凝土动力尺寸效应的规律和机理认识不足，需要在这方面进行深入研究，正确理解实验室条件下混凝土动力名义强度与大坝混凝土实际强度之间的关系，以更合理地将之应用于大坝动力设计和安全评价。本文定义了在动力荷载作用下，混凝土动力力学性能的应变率相关和尺寸相关特征为尺寸率效应；开展了不同尺寸混凝土试件动力试验，探索混凝土动力劈拉强度尺寸率效应规律；基于物理试验与数值模拟相结合的方式，进行中高应变率条件下混凝土动力劈拉性能研究，提出等效动量方法，分别就惯性效应和多裂纹扩展对尺寸率效应的贡献进行定量分析，揭示了混凝土动力尺寸率效应机理；此外，对80年老坝混凝土静动力学性能进行试验分析，探索大坝混凝土长龄期力学性能演变规律。论文主要研究工作和创新成果有：1. 系统地完成了3.5×10-7~12 s-1应变率范围的混凝土动力劈拉尺寸率效应试验，揭示了混凝土动力劈拉强度尺寸率效应规律，给出了混凝土劈拉强度准静力尺寸效应与动力尺寸效应的应变率阈值范围，修正了混凝土强度尺寸率效应公式，能够兼顾应变率相关和尺寸相关特征。2. 基于混凝土粘结颗粒元细观仿真方法，提出圆盘动力劈拉等效动量方法，定量评价惯性效应和多裂纹扩展对混凝土动力劈拉强度增长的贡献，揭示了混凝土尺寸率效应机理，发现中高应变率条件下惯性效应是动力尺寸效应的来源，阐述了混凝土劈拉强度尺寸效应随应变率发生变化的原因。3. 定量分析了混凝土动力劈拉名义强度、真实强度和等效惯性强度的关系，提出真实强度作为混凝土材料动力强度指标的建议，给出C30混凝土材料强度率相关公式。4. 对80年丰满老坝内部混凝土芯样进行了静、动力试验研究，结果表明老坝混凝土具有良好的耐久性，老坝混凝土具有与相同标号的新浇混凝土相似的静动力力学特性。
The dynamic characteristics of concrete material is of great concern in the safety evaluation of concrete dams under dynamic loading. Due to the existence of large size aggregate in dam concrete, large size specimens must be used in the test. However, there are few researches on the dynamic impact behavior of large size concrete specimens. There is limited knowledge of the dynamic size effect, and, little, if any, research has been touched on the root causes of this phenomena. It is necessary to conduct in-depth research in this aspect, in order to understand the relationship between the dynamic apparent strength of concrete under laboratory conditions and materials strength of dam concrete in the structure, and lay a foundation of the safety evaluation of concrete dam under dynamic loading.In this investigation, the size-rate effect is defined as the dynamic size effect related to different strain rates. The dynamic experiments are conducted with concrete specimens in different sizes and the size-rate effect on splitting tensile strength of concrete is revealed. The experimental tests and meso-scale numerical simulation are performed to study the dynamic impact characteristics of concrete under medium and high strain rates. Further, an equivalent momentum scheme is presented for quantitative evalution of inertia effect and influence of multi-cracks propagation on size-rate effect of concrete. Lastly, the experimental investigation on long-term mechanical characteristics of dam concrete in old Fengman Dam, which is an 80-year-old gravity dam in China, is conducted. The main research work and innovation achievements are as follows:1. The experimental investigation on dynamic splitting tensile behavior of concrete is conducted, under the strain rates of 3.5×10-7 s-1 to 12 s-1. The size-rate effect of dynamic splitting tensile strength of concrete is revealed. The range of strain rate threshold value is given, beyond which the quasi-static size effect on splitting tensile strength of concrete is inverted to the dynamic size effect. The size-rate effect formula of splitting tensile strength of concrete is proposed, which take the strain rate effect and dynamic size effect on the enhancement of dynamic splitting tensile strength into consideration.2. The meso-scale bonded-particle model of concrete disc is built, in which three-phases, namely coarse aggregates, mortar matrix and ITZs, are considered. The equivalent momentum method of dynamic splitting tensile tests is proposed to quantitatively analyze the contribution of inertia effect and influence of multi-cracks propagation on the growth of dynamic spltting tensile strength of concrete. The mechanism of size-rate effect of concrete is revealed. It is found that inertia effect is the root cause of dynamic size effect at medium and high strain rates.3. The relationship among apparent strength, true strength and equivalent inertia strength of concrete under dynamic splitting tension loads is analyzed quantitatively. The suggestion is proposed that effective strength is a better index to evaluate the dynamic strength of concrete materials, compared with apparent strength. The rate formula of materials strength of C30 concrete.4. The static and dynamic mechanical properties of aging dam concrete in the 80-year-old Fengman Dam are tested. The experimental results show that the durability of dam concrete is good. The static and dynamic mechanical characteristics of aging dam concrete is similar with 28-day laboratory concrete with same strength grade.
