| Masonry structure with a long-history has widely been used all over the world because of its features of easy availability, convenient construction processes, and low cost. Fundamental and applied researches have been done in depth in many countries, such as Canada, the United States, China, France, Italy, and so on. Among these studies, cracking and cracking control have attracted a lot of attention. It is generally accepted that the different settlement of the ground, temperature variation, and loading force have the fundamental effects on the formation and development of cracks in masonry structure. In some developed countries, creep resulting from vertical loads has been considered as one of the main reasons for increasing the deformation of masonry structure. Anyway, research work on the influence of vertical loads in masonry structure is quite limited in the world. Therefore, the present work deals with the first attempt to investigate the behaviors and mechanism of roof cracks in multi-level masonry building with the different vertical loads based on a project financially supported by the Construction Bureau of Hunan Province and Construction Committee of Changsha, China. In this paper, the behaviors and mechanism for the formation and development of roof cracks in multi-level masonry building have been studied in depth both theoretically and practically. The methods and technologies for roof cracking control have also been suggested. Additionally, numerical models and the related design methods have been proposed and further been tested by the three real masonry models. The valuable results achieved in this paper are outlined as below:â… . Experimental work has been done to investigate the masonry strength and anti-cracking ability under pressure in different periods. An optimal construction time schedule has been suggested based on the experimental results, which quantitatively address the relationships among masonry strength, anti-cracking ability and loading period.â…¡. An overview has been given on the available stress-strain theoretical analyses, standards and specifications about masonry damage and failure, theories of creep deformation. Based on the integration analyses and discussion, a newly modified theoretical model and its corresponding calculation formula for the maximal shear stress at the roof of masonry structure have been proposed at the first time. Further on, the parameters in the proposed calculation formula have been determined based on alarge number of tests.III. In order to verify the validation of the above proposed formula, three real in house made masonry models have been designed and built up based on the real situation of masonry building. Cracks and their development behaviors at the roof of the three real masonry models have been investigated in depth by changing the masonry type and mortar strength with the influence of different vertical loads. It is found that the testing results of the real models are in good agreement with the theoretical analyses resulting from our newly proposed theoretical formula. This demonstrates that the modified model and the newly theoretical formula proposed by us are reasonable and practical.IV. To further clarify the rules of cracks and their development behaviors due to the influence of different vertical loads at the roof of masonry structure, ANSYS numerical analysis method has been applied to study the crack behavior based on the stress-strain features in masonry structure. The numerical analysis results are amazingly in agreement with the test results. According to the above theoretical and experimental studies, some valuable suggestions are given for cracking control in terms of masonry design. Therefore, the fundamental and experimental results achieved in the present work will be valuable and helpful for the complement and modification of the cracking control methods and technologies in the National Design Codes for Masonry Structure, China.V. Some crack repair and cracking control methods have also been suggested to deal with the crack problems due to the different vertical loads based on the comprehensive consideration of newly developed organic and inorganic materials and practicability. Additionally, future work and its expected results are also presented in this work.All in all, the present work is not only useful for improving the reliability of masonry design, the safety and efficiency of masonry construction, and the stability and lifetime of masonry building, but also helpful for strengthening the fundamental research on the vertical deformation of masonry in China. Therefore, this work will be valuable for theoretical study and benefit to the society.
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