Buckling Analysis And Optimization Design Of Ribbed Stiffener Shallow Spherical Shell

The large-span roof for greater volume gasholder have emerged with the requirement of the of industry development. Ribbed stiffener shallow spherical shell is a form of spatial structure with plate and ribs working together. It has been widely used in modern gasholder industry for its good mechanical performance and economic application. However, be lack of theoretical research and design experience, it has brought more security risks for its practical applications. Through the theoretical analysis and numerical simulations, the buckling effect factors of ribbed stiffener shallow spherical shell are studied, the fitting formula of stability bearing capacity is obtained, the optimize design of the structure is given. The main the research content and results are as follows:1. The bearing capacity of the ribbed stiffener shallow spherical shell roof is checked. According to the engineering data of a 100,000m3 gasholder in east China, the FEM model of roof structure is established. The arc length method is used on the nonlinear stability analysis on the bearing capacity of the structure, and the critical buckling load of the structure is obtained. Then the structure static analysis is taken. By comparing the calculation results of stability and static bearing capacity, the instability is the reason that causes the ribbed stiffener shallow spherical shell structure to lose the bearing capacity.2. Buckling factors of the ribbed stiffener shallow spherical shell is analyzed. Based on the analysis conclusion of bearing capacity, 36 the basic models are selected. The arc length method is used on the nonlinear buckling analysis on the structure with the first order buckling mode as the initial form. And the critical buckling load of the structure is obtained. The influence level of section size, boundary condition, initial defect and rise span ratio and other factors on the structure instability is investigated. The research results show that: curvature radius and section size are the main factors affecting the instability of structure, the influences of boundary conditions and initial imperfections on the structural stability are not obvious.3. The calculation formula of stability bearing capacity for the ribbed stiffener shallow spherical shell structure is developed. Through the quantitative analysis of the relationship between the radius of curvature, the equivalent membrane thickness, the equivalent bending thickness and the critical buckling load, fitting the buckling critical formula by using the least square method, analyzing and selecting the safety factor, the calculation formula of characteristic value of stability allowable bearing capacity is obtained.4. The optimization design for ribbed stiffener shallow spherical shell roof is taken. With minimum amount of steel as target function, with the member size, section area and curvature radius as design variables, with the value limits of design variables as the geometric constraint, with the allowable bearing capacity of structural stability as the stability constraint, genetic algorithm is used to get the optimal solution. The reasonable configuration for the section size of member and the rise span ratio is realized.