| With the acceleration of urbanization in China,urban underground space has also been developed on a large scale.The height of the building structure continues to increase,with more and more high-rise and super-tall buildings.Therefore,the burial depth of foundations is increasing.In addition,the number of independent underground structures such as underground shopping malls and underground garages is also increasing.In areas with high groundwater levels,the underground structure faces the problem of anti-uplift.If the buoyancy of groundwater is not handled properly,it may cause damage to underground structural components,or even engineering accidents in which the entire structure is damaged.In the actual anti-uplift design,the influence of the upper load,groundwater buoyancy and foundation stiffness on the anchor stress and raft deformation uniformity should be considered.At present,in the design of anti-uplift anchors for underground structures,the anti-uplift anchors are usually uniformly distributed throughout the raft bottom.Due to the different ways of groundwater buoyancy and upper load acting on the rafts of underground structures,the stress of each anchor rod will be uneven if the anti-uplift anchors are distributed all over the raft.Therefore,a more reasonable design method is to divide the raft into two areas,and the area where no anti-uplift anchor is arranged at the bottom of the column and its surrounding area is the upper load affected area.In this thesis,the reasonable layout of anti-uplift anchors in the bottom of underground structure is studied.The main contents and results of the thesis include the following sections:(1)The principles and process of anti-uplift design for underground structures are reviewed and summarized.The differences in load classification of groundwater buoyancy,anti-uplift stability check calculation,and anti-uplift anchor technology design calculation methods in the relevant literature and codes for structural anti-uplift are compared.(2)Two kinds of division methods of upper load affected area are proposed based on the bottom soil reaction and the bending moment of the raft respectively.A two-story underground structure with raft foundation was analyzed by using the finite element method(FEM).The influences of factors such as raft thickness,column axial force,groundwater head and other factors on the bottom soil reaction were calculated by the FEM model and the main characteristics of the upper load affected area on the raft under the column divided by the two methods were analyzed.(3)Four different layouts including the anchors are a uniformly distributed throughout the raft bottom and non-uniformly distributed outside the upper load affected area under columns were considered respectively.By comparing the results of variation coefficients of the force on the anchors and the deformations of the raft under the four different distribution ways of anchors,it can be shown that non-uniformly distributed anchors outside the upper load affected area work better.By using the different thickness of the plate,the two ways of dividing the upper load affected area are compared,which shows that the upper load affected area determined by the bending moment is more reasonable.The analysis methods and conclusions on the layout of anchors in this thesis can be used as references for engineering design. |
