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Analysis and Research on Interaction Among High-Rise Building Superstructure, Raft Foundation and Ground

Author: XiaoQiang
Tutor: DingCuiHong
School: Zhejiang University of Technology
Course: Geotechnical Engineering
Keywords: Interaction Superstructure Raft foundation Ground Finite element Differential settlement Foundation reaction
CLC: TU973.31
Type: Master's thesis
Year: 2010
Downloads: 99
Quote: 1
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Abstract

With a large number of high-rise buildings being built and rapid development of computer technology, the subject about superstructure-foundation-ground interaction increasingly becomes a research focus in the civil engineering field. The conventional design method which is widely adopted by the civil engineering circles neglect the interaction among superstructure, foundation and ground, as thus the design for superstructure of the buildings is insecure, at the same time the design for foundation is rather conservative, and there are great differences between calculation result and actual case.Firstly, the thesis introduces the commonly used soil model in the interaction analysis and discusses the problem about the selection of the soil model , and then describes the basic theory and analysis methods of superstructure-foundation-ground interaction. The thesis also introduces the method which uses the FEM software, ANSYS to establish the three dimensional finite element analysis model. Finally, three dimensional finite element analysis model of frame-core tube structure-raft foundation-groundsill interation system and frame structure-raft foundation-groundsill interation system are established by using the FEM software, ANSYS, the characteristics of the two interation systems under the vertical load is study. The main contents in the thesis are as follows:1. The analysis models of the interation system which are established according to the conventional method and according to the method considering the interaction, are calculated by using the software, ansys. And then the superstructure’s internal force, the raft foundation’s internal force, the raft foundation settlement and the foundation reaction which is calculated according to the conventional method is compared with those which is calculated according to the method considering the interaction.2. The construction process of the superstructure is simulated by using the“element birth and Death”technique of the software, ansys. Then the influences which forming gradually of the superstructure stiffness exerts on the interation system are analyzed.3. Changing raft thickness and soil deformation modulus, the influence is analyzed which the variation of raft thickness and the variation of soil deformation modulus exert on raft foundation settlement , foundation reaction, the raft foundation’s internal force, the superstructure’s internal force.4. The variation characteristics of raft foundation settlement, foundation reaction, the raft foundation’s internal force, the superstructure’s internal force are discussed when the superstructure form is frame structure. And the aforementioned characteristics are also compared with the characteristics of interation system which the superstructure form is frame-core tube structure.According to the above-mentioned analysis and research, the main conclusions are as follows:1. After considering the interaction, the internal force of corner column and side column increases obviously, and the load range of corner column is greater than the load range of side column. At the same time, the internal force of the core tube and the interior column decrease obviously. The loading effect of superstructure component is quite obvious in the lower floors. In upper floors, the loading effect and the unloading effect are tend to be decrescent.2. raft moment and differential settlement which is obtained according to the conventional method are obviously less than the results which is obtained according to the method considering the interaction.3. The superstructure stiffness is limited, after having constructed a certain floor, the load range of corner column and side column, the unloading of interior column are tend to be a stable value.4. The increase of raft thickness may effectively reduce the differential settlement of raft foundation, thus reduce the additional stress in superstructure, but as raft thickness increasing, the effect is gradually weakened to reduce the internal force of corner column and side column.5. As soil deformation modulus increasing, the decrease of raft differential settlement is not obvious, and the speed of differential settlement decreasing gradually slow down. The effect which increasing of soil deformation modulus to reduce the internal force of superstructure frame column isn’t also obvious, and the effect is gradually weakened with soil deformation modulus increasing.6. When raft foundation under frame structure is analyzed, the frame column of superstructure can’t be regarded as fixed support, and internal force of raft foundation can’t be calculated according to strip method and inverted floor method, otherwise the obtained results should be deviate from the actual case.

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