Research On The Static Performance Of A Large Ribbed Stiffener Shallow Spherical Shell

Ribbed stiffener shallow spherical shell is a form of spatial structure with shell and ribs working together.It has been widely used in storage tanks for its good mechanical performance and economic application.However,be lack of theoretical research and design experience,it has brought certain difficulty to engineering design.By means of numerical analysis,model test and theoretical study,the static bearing capacity of large ribbed stiffener shallow spherical shell was studied in this paper.Firstly,based on the analogy method of elastic foundation beam,the calculation formula of the displacement and internal force of longitudinal rib were proposed.Secondly,three scaled test models were designed and fabricated,and the mechanical properties of shallow stiffened shell were analyzed through the test results.Finally,considering the influence of the initial defect,based on the relative initial defect,the formula for calculating the displacement and stress of the longitudinal rib were proposed.The main the research contents and results are as follows:1.Analyze the stress characteristics of large ribbed stiffener shallow spherical shell.The finite element models of the actual roof and the scale test structure were established,and the static analysis results of them were in good agreement,which indicated that the simplified design method of the scale test model was reasonable.By comparing the stress values of the top shell obtained from the finite element analysis data and the formula in the literature,it was found that the formula of the internal force of the open shell could be regarded as the membrane force of the stiffened shell.2.The simplified calculation method of internal forces for shallow ribbed ring stiffened shell was studied.Considering the lateral support provided by the circumferential rib and the spherical shell membrane stress to the longitudinal rib,the calculation formula of the longitudinal rib internal force and displacement was derived based on the analogy method of elastic foundation beam.Considering the shear lag effect of the flange,the calculation method of the effective width of the combined section of stiffened rib and the principle of segmental taking value were studied.The calculated displacement and stress of the two scaled models were in good agreement with the results of finite element method.3.The mechanical properties of ribbed stiffener shallow spherical shell structure were analyzed through static load test results of the scaling models.The experimental results of the three scaling models showed that the deformation and stress of the structure basically conformed to the linear relationship before reaching the elastic limit load,and the initial defect was the key factor for the local instability and the overall instability of the structure.The deformation and stress of the three scaling models all meet the design requirements of the gas tank roof under normal working load.4.The calculation method of vertical displacement and stress of longitudinal rib under the influence of relative initial defects were studied.According to the initial defects of the test models and vertical displacement and strain data of the key points on the longitudinal ribs,introducing the concept of relative initial defect of stiffened shell,the parameters k andη were fitted,the vertical displacement and the stress calculation formula were derived with initial defects.Compared with the test values of the three models,the calculated values were in good agreement with the test data.