Strength and Long-term Behaviour of Masonry

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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.