Theoretical And Application Research On Seamless Construction Of Mass Concrete

The box foundation, raft foundation and pile caps in engineering structure usually with bigger thickness or area are mass concrete, in the casting phase the temperature load caused by the hydration heat and its shrinkage property will produce great thermal stresses, which will cause hazardous cracks if design and construction are inappropriate. In the past, we adopted expansion joints and post-pouring zone to solve this problem; but due to such reasons as the integrity of the building and structure, serviceable function and demand of construction time of a project etc., we put forward the requirement of seamless construction to these structures, that is to say, the requirements of design and the quality of construction can still be satisfied without adoption of expansion joints and post-pouring zone in the construction phase.At present, the researches on seamless construction of the mass concrete structures were relatively deficient in domestic and foreign countries, most designs and constructions strongly depended on past engineering practices and experiences, and lacked necessary theoretical support and guides; as a result, a large amount of waste or loss may be caused and possibly some hidden dangers are present in projects' quality, thus which will influence the reliability of structures, so it is urgent to launch the theoretical and application research into this topic.On the basis of the analysis and summaries of seamless construction methods, combined with the design of seamless construction plan on Xi'an Wanda commercial plaza's raft foundation, in this paper the seamless construction measure by releasing the stress in short-range is addressed, the theoretical basis for the sequential placement is given, the calculation method of the thermal stress and its distribution rule by the use of the construction method presented in this article are studied, and a large-scale finite element program ANSYS is utilized to simulate and analyze its thermal stress in construction and operation phases. The main research contents include the following aspects: (1) Based on the existing research findings, analyzed the mechanism and rules of temperature cracks of mass concrete, selected a reasonable calculation model and performed an analysis of the thermal stress with the seamless construction, proposed the calculation method of thermal-shrinkage stress and partitioned size under the sequential method.(2) Combined with the project example of mass concrete structure, the raft foundation structure of Xi'an Wanda commercial plaza, the use of the method presented in this paper carried on analysis on the thermal stress and cracking fracture checking in the construction phase, verified the reliability of the advanced method.(3) The use of the finite element analysis program ANSYS, simulated the thermal and shrinkage stress of Xi'an Wanda commercial plaza during construction and operation phases, obtained the corresponding distributions of temperature field and stress field. Compared to the theoretically calculating results, they are in a good agreement.The research results indicate that the method presented in this paper can better reflect the thermal stress state of mass concrete structures, and exhibit a better applicability; it can supply the theoretical support for their design and construction of mass concrete foundation for homogeneous structures, and then it can be referred to by engineering projects.