Crack Mechanism And Controlling Technique Of High-rise Building Basement Wall

In these years, with the increase of the number of high-rise building in cities, temperature cracks of basement wall draw more and more public attentions. How to solve this problem has become a difficult nut in the engineering practice and needs urgent solutions to meet engineering demands. As a sub-topic of "cracking mechanism and a whole set of control technique of modern concrete ,structure"(NO:50278031) supported by national natural science foundation, this paper studies ail-roundly and systematically temperature crack controlling technique of basement wall of high-rise building and puts forward the solution methods into the theoretical calculation and construction practice.The main work done in this paper is as follows: (1) simulate the temperature field of basement wall by ANSYS software, sum up the characteristics of the temperature field of basement wall, and analyze the influence of the types of the molding board, environmental change and cement content; (2) the whole simulation analysis process of early-age concrete stress field is realized by sub-development of ANSYS, and CTS-ANSYS software is developed with Fortran; (3) based on the cause of cracking, the influence of the thickness of the wall, length, bar arrangement, mix proportion, expanding agent, etc, on the wall stress due to concrete creep and temperature change is analyzed.On the basis of the research work mentioned above, some crucial conclusions are acquired as follows: (1) the temperature in the basement wall changes quickly, reaching maximum temperature in 24 hours and after 7 days being the same as the temperature outside the wall; (2) the normal stress is the control stress which causes cracks in the basement wall; (3) when we use steel molding board to support wall, creeping thermal stress is small and tensile stress appears early; (4) if the basement wall is thin, the creep stress is small and tensile stress appears early; (5) the longer the basement wall is , the larger the creep stress is. But when the wall length exceeds a certain length, the normal stress would not increase; (6) the change rule of the basement wall creep thermal stress has close connection with the modulus of elasticity and creep characteristics. If the modulus of elasticity changes slowly and early stage creep slack is large, the tensile stress will be small; (7) in hardening process, the self-stressing concrete added expanding agent can produce compressive pre-stress in the wall to reduce tensile stress; (8) frame columns and embedded columns have strong restriction, and we can use those columns to restrict free expansion, and to change free expansion into efficient expansion.By analysis and study, the methods of controlling the thermal crack in basement wall have been summed up in design, material supply and construction. These methods have been applied in Wuxi Development Building basement wall project, and a series of efficient measures methods have been proposed.