Calculation Parameters Analysis And Design Optimizations To Raft Foundation Of High-rise Structure

Because of the advantages of high stiffness, good integrity and good resistances to earthquake, raft foundation has been widely applied in construction projects. Owing to the reasons of raft’s force-deformation complexity, it’s necessary to have a further research. In pratical projects, thickness and reinforcements may be variable designed by different engineers, it would cause material waste or security flaw. Based on pre-existing calculation and analysis theory and design method of raft foundation, reasons of material waste, security flaw and present relevant optimal methods have been analyzed in this article. The whole thesis consists of three parts:1) By using the finite element method, effect of superstructure, friction of foundation soil, lateral soil-pressure and buoyancy of groundwater on raft foundation have been reserched, and puching shear capacity is also analyzed. The conclusions are as follows:(1) The stiffness of superstructure has great influence on the deformation of raft foundation. When the superstructure is frame structure, it’s necessary to consider the effect of construction process to deformation of raft foundation.(2) When the superstructure is frame structure and raft depth is less than one meter, friction of clay and silt should be considered. In other cases, frictional slipping can be ignored.(3) when effect of stiffness of superstructure has been considered, lateral soil-pressure can be ignored.(4) In calculation of raft foundation under buoyancy, compressed-spring model should be used to simulate foundation soil or nonlinear analysis.(5) The highest level of concrete used in raft foundation should be C40. Stirrup has a better result than bent-up steel to improve the punching shear capacity. Bent-up steel should not be used if raft depth beyond 1200mm.2) By using finite element method, effect of the rebar to hydration in raft foundation is reserched. Conclusions are as follows:thin bi-directional rebar in top surface of raft foundation is better than the thick one to improve the crack resistance ability. Bi-directional rebar in middle of raft foundation is no use to improve crack resistance ability.3) Combined with practical projects, design optimizations about the arrangement, thickness, reinforcement and concrete of raft foundation has been put forward in this article, in order to meet the goal of reasonable stress and economical cost.