Finite Element Analysis On The Under Column Pier Of Raft Foundation In Basement

In recent years,with the rapid increase in the number of vehicles,the needs of commercial development and the requirements of civil air defense,the basement garage is widely used in all kinds of buildings(especially high-rise buildings).The flat raft foundation has the advantages of shallow buried depth,simple construction technology,short construction period,high utilization ratio of basement space,etc.,which is one of the basic forms of basement floor design.The calculation method of internal force and reinforcement of flat slab raft foundation can be divided into inverted floor method and elastic foundation plate method.When the foundation is relatively uniform,the upper structure stiffness is good and the change of column load and column spacing are less than 20%,the inverted floor method can be chosen;when the foundation is more complicated,the upper structure stiffness is poor or the change of column load and column spacing are large,the elastic foundation plate method should be chosen.Elastic foundation plate method is relatively accurate,but because of the complexity of the foundation soil,neither the Kerr assumption nor the infinite elastic body assumption can reflect the actual situation of the foundation well,and the mechanical index of soil used in the calculation(such as foundation coefficient and elastic modulus)are difficult to be determined accurately,so the results often differ from real situation.Therefore,the actual settlement basis can be used to calculate the foundation coefficient K.Then the elastic foundation plate method can be analyzed to get the appropriate reinforcement.This paper takes the East Building of a university's comprehensive teaching building as the research object,making the raft foundation analysis through the following works:1.The raft plate of the lower column pier is regarded as an inverted floor without beam,and the lower pier as inverse column cap.The raft foundation is calculated by the method of non beam floor,and the internal force of raft foundation is calculated and analyzed.2.The foundation settlement from geological investigation data is adopted to calculate the coefficient of subgrade reaction K.Then the elastic foundation plate method is adopted to make finite element analysis on the raft.The influence of the stiffness of the superstructure and the grid size on the reinforcement of the raft isanalyzed.3.The inverted floor model is adopted to make finite element analysis on the raft to get the reinforcement.Then the result is compared with that of the elastic foundation plate method.And the causes of the differences between the results are analyzed.4.On the premise of ensuring the same parameters,the influences of the change of the thickness of the column pier on the internal force distribution and the reinforcement of the raft are observed.Then find out the reasonable thickness of the pier and optimize the reinforcement of the raft.Based on the above analysis,the reinforcement calculated by the coefficient of subgrade reaction K from foundation settlement combined with elastic foundation plate method is most economical and reasonable.Under certain premise,increase the thickness of pier reinforcement appropriately can also optimize the raft reinforcement.