Research On Internal Force And Deformation Of Multilayer Ring Beam Supporting Structure In Deep Foundation Pits

With the rapid development of urban construction,foundation pit engineering has been gradually becoming deeper and bigger,as a more reasonable force,multi ring beam supporting structure has a rapid development,which is able to provide more space for support system.In theory,the analytic solution of the ring beam is already there under the symmetrical load,but the stress analysis of the ring beam under eccentric loads has not been well solved yet.As a tarting point from the theories of structural mechanics and elastic mechanics respectively,this paper discusses the theoretical solutions of the ring beam under eccentric loads and makes some numerical simulations using MIDAS GTS that is a finite element software for the deep foundation pit with ring beam retaining structure of redevelopment project in Wuhan zhongsheng urban Village,getting the internal force and deformation behavior of ring beam retaining structure and putting forward reasonable suggestions and measures to reinforce the beam retaining structure.The main research results are as follows:(1)To study the uneven stress of ring beam problem with the structural mechanics thinking,simplify the uneven stress to the sum of local uniform and whole uniform load,obtain the internal force equation of local uniform load by force method.(2)According to the ring beam subjected to the eccentric load of q(1+2ksin~2?),by using the Fourier series expansion,the semi inverse solution of elastic mechanics and the complex variable function method,the analytical solution of the eccentric load is obtained.(3)Midas GTS numerical analysis software are used to simulat and analysis,get the result that ring beam supporting structure in the midpoint of each sides of the pit are suffered negative moment(inner tension,for one layer the maximum is-1303kN·m,second layer maximum is-1315kN·m),corresponding to the corners of the foundation pit of the ring beam are suffered positive moment(lateral tension,for one layer the maximum is 822kN·m,second layer maximum is 1069kN·m);When two ring beam structure are used,axial force and bending moment on the inner ring beam were significantly bigger than the outer ring beam;The ring beam supporting axial force is directly proportional to the radiation beam axial force.(4)The maximum of radiation axial force of Ring beam retaining structure is1006kN,and the minimum is 474kN,radial support axial force are all under pressure;the maximum of gusset and brace support axial force of beam support structureis3885kN,the minimum value is-1823kN(in tension),the difference of them is quite great,but the section of supporting beam are all the same for 1200mm×800mm in the design of supporting parameters.It is a huge waste of using the same beam section.Unreasonable design of supporting structure was often appeared.Caused local stress concentration phenomenon.The ring beam is subjected to large axial force.The axial force distribution of radiation support is more uniform.So it is a kind of more reasonable supporting form.