基于断裂能量释放理论的轻骨料混凝土深受弯构件受剪尺寸效应机理研究

Lightweight aggregate concrete (LWAC) is prone to aggregate fracture due to the lower strength of lightweight aggregates compared with cement matrix, and its brittle feature and size effect behavior are more significant than that of normal weight concrete. The existing size effect theory based on the aggregate interlock mechanism becomes inapplicable, while the energy release theory in fracture mechanics is an effective means to solve the size effect problem of this kind of concrete. This project focuses on LWAC deep flexural members, and intends to establish the relevance between the energy release rate at the meso-cracks and the size effect of macro members started from the research of fracture behavior of materials and components. By studying the fracture damage process and fracture energy parameters quantization of LWAC, a two-dimensional random aggregate model considering the aggregate fracture mechanism will be established, and then a unified expression of fracture energy that is capable of charactering the material features and contains physical meanings can be proposed. The influence of key parameters on the damage evolution law of fracture band zone in LWAC deep flexural members is analyzed. Thereafter, the calculation model for the effective width and height of fracture band zone can be determined by using the fracture energy of material and the strut-and-tie shear transfer mechanism. The quantitative relationship between the energy release rate of fracture band zone and the nominal shear strength of members is constructed to reveal the size effect mechanism of LWAC deep flexural members, and moreover, the corresponding shear analysis model is established based on the energy release equilibrium. The research is of both theoretical significance and practical value for enriching the design theory of large-size concrete members and promoting the engineering application of LWAC.

轻骨料混凝土中骨料强度较水泥石强度低，易发生骨料破坏，脆性突出，相比普通混凝土尺寸效应更加显著。对该类混凝土尺寸效应问题现有基于骨料咬合机制的尺寸效应理论不再适用，断裂力学能量释放理论是解决的有效手段。本项目针对轻骨料混凝土深受弯构件，拟从材料与构件的断裂行为特征出发，建立细观裂纹处能量释放速率与宏观构件尺寸效应的关联性。通过研究轻骨料混凝土断裂破损过程与断裂能参数量化，建立骨料破坏机制下的细观二维随机骨料模型，提出可表征材料断裂特征且具有物理意义的断裂能统一表达式；明确关键参数影响下轻骨料混凝土深受弯构件断裂带损伤演化规律，利用材料断裂能与拉压杆剪力传递机制确定断裂带有效宽度和高度计算模型；构建断裂带能量释放速率与构件名义抗剪强度的量化关系，揭示尺寸效应机理，基于能量释放平衡建立受剪分析模型。研究成果对于丰富大尺寸混凝土构件设计理论、促进轻骨料混凝土工程应用均具有重要理论意义与实用价值。

轻骨料混凝土中骨料强度较水泥石强度低，易发生骨料破坏，脆性突出，相比普通混凝土尺寸效应更加显著。对该类混凝土尺寸效应问题现有基于骨料咬合机制的尺寸效应理论不再适用，断裂力学能量释放理论是解决的有效手段。本项目针对轻骨料混凝土深受弯构件，从材料与构件的断裂行为特征出发，建立了细观裂纹处能量释放速率与宏观构件尺寸效应的关联性。研究了轻骨料混凝土断裂破损过程与断裂能参数量化，提出了反映材料断裂特征的断裂能统一表达式；分析了关键参数影响下轻骨料混凝土深受弯构件断裂带损伤演化规律，揭示了该类构件的尺寸效应作用机理，基于拉-压杆理论和断裂力学理论完成了深受弯构件的受剪模型化分析，并提出了相应设计方法。研究成果对于丰富大尺寸混凝土构件设计理论、促进轻骨料混凝土工程应用均具有重要理论意义与实用价值。