Settlement And Stress Analysis Of Foundation Raft Under The Combined Action Of Frame-shear Structure And Foundation

In conventional design,the superstructure,foundation and soil are often considered separately.First fix the bottom of the superstructure,calculate the internal force at the bottom of the structure,and then apply the internal force to the foundation to calculate the reaction force of the foundation.Assuming that the reaction force of the foundation is linearly distributed and reacts on the foundation,the internal force and deformation of the foundation are obtained.However,as the number of building structure layers increases,the deviation between the results calculated by conventional design methods and the internal force and deformation of the actual structure becomes larger and larger.It is particularly important to consider the problem of the interaction of the superstructure,foundation and foundation.This paper summarizes the research results on the problem of interaction at home and abroad,and establishes a structural model that does not consider the interaction and the consideration of the interaction through the MIDAS/GEN finite element software,and conducts a comparative analysis;at the same time,the effect of the structure on the gravity load and Under the action of earthquake,we can check whether the structure meets the specification requirements by changing the number of layers of the structure,the thickness of the foundation raft,the overhang length of the foundation raft,the concrete strength of the foundation and the stiffness of the foundation;The influence of superstructure,foundation and foundation.And through the modeling and analysis of finite element software,the relevant standard formulas are revised,and verified through two actual projects.This thesis mainly carried out research work in the following aspects:(1)The MIDAS / GEN finite element software is used to establish a structural model that does not consider the interaction and considers the interaction,and conducts a comparative analysis to conclude that when considering the interaction,the axial force ratio of the column in the bottom of the upper structure does not consider the common When the action is 24% smaller,the axial force of the bottom shear wall will increase by more than20%,and after considering the joint action,the bending moment of the bottom column of the superstructure will change significantly.That is,after considering the joint action,due to thedifference in the settlement of the bottom of the structure,the internal force at the bottom of the structure changes significantly after the internal force redistribution occurs in the structure.(2)Under the action of gravity,by changing the parameters of the superstructure layer,the thickness of the base raft,the overhang length of the base raft,the strength of the foundation concrete,and the stiffness of the foundation,it is found that with the number of superstructure layers The increase in the difference in settlement at the bottom of the structure increases,the more obvious the internal force redistribution of the structure,the more the load is transferred to the shear wall;the increase in the thickness of the foundation raft changes the foundation from flexible to rigid,which can make the foundation The internal force distribution is more uniform,and at the same time can reduce the settlement of the foundation.When the thickness of the foundation raft is 1.2 meters,the settlement of the foundation is basically unchanged;the overhang length of the foundation mainly affects the stress and settlement of the edge area of the foundation,and the influence on the central area is more Small;the increase in the strength of the foundation concrete has less effect on the stress and deformation of the structure and the foundation;the increase in the rigidity of the foundation,relative to the rigidity of the superstructure and foundation,increases the proportion of the load it bears and reduces the foundation raft.Internal force,and make its distribution more uniform,while increasing the reaction force of the foundation.(3)Under the action of earthquake,eight ground motions are selected for analysis.At the same time,the influence of factors such as foundation raft thickness,foundation overhang length,and foundation stiffness on the structure is studied under rare earthquakes.Increasing the thickness of the raft increases its own stiffness,at the same time,it improves the ability of the foundation to resist its own irregular deformation under the action of rare earthquakes,and promotes the stress diffusion of the top / bottom of the foundation raft,reducing the range of the zero-stress zone.The increase in the overhang length of the foundation raft makes the stress of the center of the foundation raft under a large earthquake increase,and the stress at the edge shows a fluctuating change,which reduces the maximum settlement of the foundation raft under a large earthquake and slightly reduces the base Zero stress zone range;the increase in foundation stiffness will increase its stiffness relative to the foundation andsuperstructure,and the load ratio it bears will increase,while suppressing the deformation of the foundation and reducing the settlement of the foundation,but it will increase the effect of rare earthquakes.The range of the zero-stress zone of the lower base.(4)Through the results of finite element analysis,the formulas for the punching and shear capacity of the raft base plate in the code are revised,and the verification analysis is carried out through two actual engineering cases,which provides suggestions for the design of the raft foundation.