Research On The Seismic Performance Of Ribbed Annular Stiffened Shallow Spherical Shells

With the development of China’s productivity,large-capacity storage tanks are more and more widely used.Ribbed stiffened shallow spherical shells are often used in the structure of tops and pistons of gasholder due to their excellent space stress performance.As China’s requirements for seismic performance of building structures become more stringent,research on seismic performance of large ribbed stiffened shallow spherical shells is lacking.Based on the background of a 300,000 m3 cover of gasholder in East China,this paper combines experimental research,numerical simulation and theoretical analysis to analyze its natural vibration characteristics,then uses the time history analysis method and response spectrum method to study its seismic performance and discuss reasonable seismic analysis method.The main research contents are as follows:1.The study of the natural vibration characteristics of the ribbed annular shallow spherical shell.According to the engineering data of a 300,000 m3 gasholder in East China,a 1:15 finite element scale model of the roof structure is established,and the Block lanczos method is used to calculate the structural natural vibration characteristics and vibration mode.Then three scale models are made and their dynamic characteristics are tested.By comparing the finite element analysis and the test results,the structure is dominated by vertical vibration,and the first five orders of natural vibration frequency are in good agree-ment,which verifies the accuracy of the finite element model.This part of the research content draws conclusions that can be used in engineering practice,which has reference value for the selection of subsequent seismic waves and the study of seismic performance.2.Analysis of influencing factors of natural vibration characteristics of ribbed ring stiffened shallow spherical shell scale model.Through the establishment of finite element models with different support forms,opening forms,top shell thickness,and vector-to-span ratio,the effects of the changes of the four parameters on the natural frequency and mode of the structure are analyzed.The results of the study show that the influence of the form of the support is small,the influence of the thickness of the top plate and the ratio of the vector to the span is large,and the influence of the opening form is significant.3.The fitting of the simplified calculation formula of the first-order natural frequency of the open and closed rib ring stiffened shallow spherical shell.Drawing on the formula for calculating the natural frequency of smooth spherical shells,keeping the ratio of vector to span to 1:10,changing the thickness and radius of curvature of the top shell,establishing 24 kinds of finite element models,obtaining their fundamental frequency data,fitting the correlation coefficients through Origin software,The simplified calculation formula of the first-order natural frequency of the open and closed rib ring stiffened shallow spherical shell is obtained.4.Seismic response analysis of large-ribbed stiffened shallow spherical shells with time history analysis.Establish a finite element model of the solid structure of a large ribbed stiffened shallow spherical shell,and use the time history analysis method to calculate the X direction,Z direction,XYZ three directions(X direction is mainly)and XYZ three directions(Z direction is mainly)the dynamic response under the action,analyze the change law of its stress and deformation.The results show that the maximum dynamic response of the two structural forms of open and closed are located at the position of the inner ring beam and the top of the shell,respectively.The vertical(Z-direction)seismic response of the two structural forms is significantly increased compared to the other directions.For the convenience of calculation,the time-history response analysis of this type of structure can be performed with Z-direction single-dimensional earthquake action.5.Seismic response analysis of large ribbed stiffened shallow spherical shells by response spectrum method.By analyzing the structural response spectrum method of the two opening forms,the corresponding dynamic response data is obtained.The analysis results show that the fundamental frequencies of the two structures are large,the rigidity of out-ofplane is high,and the seismic performance is good.When applying the response spectrum method to the seismic analysis of the structure,the main overall vibration mode should be considered,and the influence of other local vibration modes should be ignored.6.Proposal of seismic analysis method for large ribbed stiffened shallow spherical shell structure.Comparing the calculation results of the time history analysis method and the response spectrum method of the two opening forms of the structure,it is recommended that in the seismic response analysis,the response spectrum method should be selected for the opening structure;for the closed structure,the time history analysis method and the response spectrum should be used at the same time and take the most unfavorable analysis result to judge the seismic performance of the structure.