FEM Analysis On The Structure-raft-subgrade Interaction Of A Tall Office Building

With regard to the high-rise buildings built on the soft foundation soils, the traditional method called simply analysis often results in waste or hidden danger, on the contrary, the interactive analysis method which views the up-structure, foundation and subgrade as a whole can actually reflect true working-condition of a tall building. But it is the complexity of the interactive subject that causes the civil engineering circles at home and abroad to pay highly attention to the subject.With the development of FEM (Finite Element Method) and substructure theories, the research on the interactive analysis becomes feasible with the help of the large universal FEM software and high-powered hardware of a computer. In this paper, the simply analysis model (model I ) and the interactive analysis model (model II) of the office building ,which is frame-shear wall structure, are created independently by ANSYS. First, the displacements and stress are compared of the two models under the action such as gravity force, wind load, and horizontal earthquake. Secondly, the interactive mechanism of the frame-shear wall structure is discussed by changing the parameters such as subgrade modulus (Es), raft thickness and up-structure stiffness. In the end, some beneficial conclusion is drawn as follows:1, Under the gravity action, the axial forces of the mid-side columns in model II, contrasted with model I , are visibly increased, contrarily, that of the internal ones decreased.2, Under the wind action, the lateral displacement of model II, contrasted with model I , is obviously increased, the frame contribution is enhanced.3, The modal analysis shows that not only the fundamental frequency of model II bec omes clearly slower than that of model I , but also the mode shape vector is different from model I .4, While suffering from the earthquake, the total base-shear force of model II is less than that of model I , the base-shear force applied to the shear wall of model II obviously is decreased, contrasted with that of model I5, Keeping the stiffness of foundation and up-structure invariable, the softer the subgrade is, the clearer the difference in the foundation settlement, so that, both the whole moment of the foundation and redistribution effect of stress in the up-structure are all increased.6, Keeping the stiffness of subgrade and up-structure invariable, both the difference in the foundation settlement and redistribution effect of stress in the up-structure are decreased on condition that the foundation stiffness is increased, but the foundation moment unfortunately rises.7, Keeping the stiffness of subgrade and foundation invariable, the difference in the foundation settlement will be decreased due to the increase in up-structure stiffness, but the contribution of up-structure stiffness is limited.Therefore, it is necessary that the interaction of the up-structure, foundation and subgrade is well considered in the concept design and structure design of the high-rise building. The techniques of details and measures will be taken according to the interaction in order to make the structure design safer and more economical. The conclusion of the paper will be instructive to the structure analysis and design of the similar engineering.