Strength and Long-term Behaviour of Masonry

该提案分为三个主题。首先，我建议研究最初仅沿一个方向压缩的准脆性材料中裂纹扩展的基本机制。结果不仅适用于砖石，还适用于混凝土、岩石等。在拉伸状态下，将载荷产生的应力强度与材料的断裂韧性进行比较。当前者到达后者时，就会发生断裂。压缩没有等价物，因此我们预测压缩断裂的能力比拉伸断裂的能力差得多。基本机制尚未阐明，因此我建议研究驱动裂纹扩展的能量来自何处以及缺陷形状和宽度对应力和应变能的影响。与拉伸断裂相比，裂纹宽度和形状似乎是压缩断裂的重要参数。一旦通过建模和实验工作了解了单个裂纹的基础知识，我建议研究现实中发生的多个裂纹的情况。在第二个主题中，我建议扩展一种建模技术来研究历史砖石结构随时间的应力重新分布。由于风化导致的结构外部恶化已被包括在内，但该模型需要推广，以便可以在设计办公室中使用，并在实施之前评估干预措施的效果。这项工作还将有助于更好地了解遗产结构中某些类型的裂缝模式的原因。目标是确保针对结构提出的干预措施实际上有助于结构并按预期运行。这将有助于为后代保护我们的砖石建筑遗产。在第三个主题中，建议继续进行砌体抗剪强度方面的工作。加拿大结构砌体规范中砌体抗剪强度的方程包括所考虑的单元截面上的弯矩和剪力因子。这与极限状态设计理念相反，在极限状态设计理念中，结构元件的强度仅根据材料特性进行估计，并与载荷影响的估计进行比较：强度必须大于载荷影响。因此，将检查文献中的抗剪强度测试和方程，并进行额外的测试来定义确定砖石抗剪强度的方法：将提出如何调整这部分规范的建议。对大间距钢筋砌体的研究将研究如何通过实验和建模相结合来正确预测其破坏模式和强度。总体而言，拟议的工作范围将带来更好的设计和更安全的结构，特别是砌体和遗产砌体，并为使用断裂力学方法预测受压砖石和混凝土等材料的压缩破坏奠定基础。

The proposal is split into three themes. In the first, I propose to pursue the basic mechanism(s) for crack propagation in quasi-brittle materials initially being compressed in only one direction. Results would not only apply to masonry, but also to concrete, rock etc. In tension, the stress intensity from the loading is compared to the material's fracture toughness. When former reaches the latter, fracture occurs. There is no equivalent for compression, so our ability to predict compressive fracture is much poorer than in tension. The basic mechanisms have not been elucidated, so I am proposing to examine both where the energy comes from to drive crack propagation and the effect of flaw shape and width on stress and strain energy. In contrast to fracture in tension, flaw width and shape appear to be important parameters for compressive fracture. Once the basics for a single crack have become apparent from modelling and experimental work, I propose to look at the case of multiple cracks, as occur in reality. In the second theme, I propose to extend a modelling technique to look at stress redistribution in heritage masonry structures over time. Deterioration of the exterior of the structure due to weathering has been included, but the model needs to be generalized so it can be used in design offices and the effects of interventions assessed before they are implemented. The work will also lead to better understanding of the causes of certain types of crack patterns in heritage structures. The objective is to ensure that interventions proposed for structures will actually help the structure and perform as intended. This will help preserve our heritage, as expressed in masonry buildings, for future generations. In the third theme, continuation of the work on the shear strength of masonry is proposed. The equation for the shear strength of masonry in the Canadian structural masonry code includes the factored moment and shear on the section of the element under consideration. This is contrary to limit states design philosophy in which the strength of a structural element is estimated from material properties alone and is compared to the estimate of the effects of loads: the strength has to be greater than the load effect. Thus, shear strength tests and equations in the literature will be examined and additional tests performed to define a method to determine masonry shear strength: suggestions on how to adjust this part of the code will be made. Work on widely spaced reinforced masonry will investigate how to predict its mode of failure and strength correctly through a combination of experiments and modeling. Overall, the proposed scope of work will result in better designed and safer structures, particularly masonry and heritage masonry, as well as laying the foundation for a fundamental change to predicting compressive failure of materials like masonry and concrete subject to compression - using a fracture mechanics approach.