The Research On The Effect Of Vertical Load Difference On Roof Cracking Behaviors In Multistory Masonry Buildings

In China, masonry buildings have existed over two thousand yeas since the Great Wall and ancient bridge in Zhao Zhou. As a primary structure, masonry structure has been developed quickly with the constant renewal of building materials in recent yeas. Masonry structure has following advantages:drawing materials conveniently, easy construction, economical, applicable, and so on. As the main wall materials of policy suggestion in the wall reformation, concrete hollow block gradually becomes one of most commonly used load-bearing wall materials instead of the clay solid brick.However, the craking of masonry buildings is a common problem especially on the top floor. In many factors, the different settlements of the ground, shrinkage, temperature and moisture variations are the common reasons. Whereas, there are still some cracks in the top story, especially in the intersection between the bearing wall and the non-bearing wall, even if taked enough measures in thermal insulation. Whether domestic or foreign, few researchers have made a study on cracking of masonry buildings on the top story because of vertical loads difference. Supported by National Natural Science Foundation of China (No.50778067), this thesis predominantly focues reseach on the craking behavior by the effect of the vertical load difference in concrete block masonry buildings.The main works are summarized as follows:(1) Tests on mechanical properties of thirty masonry specimens of normal concrete small hollow block are carried out to experimentally study the relationship between periods and the compressive strength, the curves of stress-strain and the effect of earlier loading to lateral strain. By experiment, earlier loading can lead to large vertical compressive deformation of masonry buildings in complex stressed state because of the low strength of motar. Therefore, it is worthwhile to pay more attention to control the construction schedule.(2)The creep theory and cracking characteristics with diverse conctrustional details are described. Based on the above-mentioned content, a model of masonry structure with the bearing wall and non-bearing walls is built. And the formula of maximum shear force is presented, of which parameters are determined by experiment.(3) According to the cracking characteristics of concrete block masonry walls with columns and ring-beams and the the formula of the maximum shear force, a six-story masonry model structure is designed and built with concrete small hollow block, which is tested to study the cracking influenced by the vertical loads difference. The disaplacements on the top of masonry and the relative deformations in lateral and vertical are experimentally studied. Meanwhile, the load deformation curves under different vertical loads of the bearing wall and non-bearing walls are analyzed and presented. Combining the maximum shear force formula with the results of masonry model experiment, the maximum shear force formula is verified to be scientific and rational by comprehensive analysis, which has a very important realistic meaning.