Research On Response Value Of Free-field Displacement About Rectangular Structure In The Underground Structure Seismic Design

Response displacement method and nonlinear dynamic history analysis method are often used for seismic design of rectangular underground structure.The reason why lots of designer uses that two methods is that they can properly show the interaction between soil and underground structure and effectively calculate the values of internal force and displacement about underground structure.However,they also have some obvious defects.For example,response displacement method includes so many parameters that the calculation is very difficult.For nonlinear dynamic history analysis method,it also takes a long time to solve a problem.So the principal purpose of this paper is to research an easy seismic deign method of rectangular underground structure.This easy seismic deign method not only have the advantages which that two methods have,but also avoid defects which that two methods have.There is an most important parameter called responsive value of free-field displacement,R,in the easy seismic design method.In this paper,the value of R is comprehensively studied.The research content mainly aimed at finding the relationship between some parameters lots of designer focus on and the value of R.That parameters include the relative stiffness of soil and underground structure,the size and the buried depth of underground structure.Among them,the flexibility ratio,F,is used for indicating the relative stiffness of soil and underground structure.The value of F expresses the objectivity about the interaction between soil and underground structure which causes the distortion of structure.In addition,this paper also defines depth-width ratio,λ,to express the size of rectangular cross-section.The buried depth of underground structure is represented by the ratio of the buried depth and height of structure.That value of expression isρ.In this paper,the research methods include theoretical analysis and numerical simulation.In theory research,on the one hand this paper draws lessons from the researches about the interaction coefficient of soil and circular underground tunnels for the contrast,on the other hand the theory of complex variables functions and elastic mechanics is used for researching relationships between R and F、R andλabout rectangular underground structure at F>20,which improves the theory about the value of R.In this paper the rule of R-F、R-λand R-ρis also analyzed by numerical simulation based on FLAC^3D.For R-F,the solution of numerical simulation is consistent with the theory in the trend.At F>20 the solution of numerical simulation is consistent with the theory in the value.At 1<F<10 the solution of numerical simulation is consistent with the past research.The above content can prove the validity of numerical simulation and further show the relationship between R and F about rectangular underground structure.For R-λ,through theoretical analysis and the regression of power function,the theoretical formula has been corrected to the approximate formula.The approximate formula not only meet the requirement of numerical accuracy,but also can be used conveniently.For R-ρ,a large number of numerical solution show the value of R about every depths can be replaced by the value of R atρ=1.At the last,this paper puts forward an easy seismic design method for rectangular underground structure.Through the comparison between the easy design method and response displacement method or nonlinear dynamic history analysis method,the result show that this easy method not only close to the that two design methods,but also less parameters is demanded to use,which indicate the purpose of this paper is achieved.In this paper the theoretical analysis provides new idea for the research on the seismic problem of underground structure,a large number of numerical data provide reference and guidance for scientific research and design,the proposed easy method for the seismic design of rectangular underground structure has practical value for engineering and design.