Form-Finding And Stability Research Of Rigid Single-Layer Lattice Shells

The sun valleys of the Expo Axis are the eye-catcher in the Expo buildings because of their unique styles and gorgeous grid mesh. There is rare research on the grid mesh of free-form surface lattice shells and stability analysis considering member buckling in China. This thesis based on sun valley, looking for a form-finding method that will find a more rational geometry for single-layer lattice shells, in other word, through the form-finding technology a new form of lattice shell with both high load capacity and architectural aesthetics will be found. The advantages of form-finding of rigid structure is confirmed by investigation on form-finding on single-layer cylindrical lattice shells,single-layer spherical lattice shells and single-layer free-form lattice shells; a stability analysis method that considering member buckling is also studied; the stability behavior of shuttle-shape steel lattice column with bending moment is fully investigated at last.Chapter 1 reviews the development history, classification and development orientation of lattice shells, the theory status of form-finding and stability analysis are studied systematically. It also introduces the background and research contents of this thesis.Chapter 2 aimed at investigating the rational form-finding problem of single-layer lattice shell structures, a form-finding method for rigid structures based on force density is proposed. The form-finding of single-layer cylindrical lattice shell with zero Gaussian curvature is realized by accounting for the self-weight of the structure during the form-finding process. Static and stability behavior of traditional cylindrical lattice shell and form-finding lattice shell are compared, and the effect of form-finding is confirmed. A new single-layer paraboloid lattice shell is proposed at last, which could be used in practical design.Chapter 3 focuses on the rational form-finding of single-layer spherical latticed gird shell structures. The form-finding of single-layer spherical lattice shell with positive Gaussian curvature is realized by accounting for the self-weight of the structure during the form-finding process. The shape of form-finding lattice shell is very close to sphere, but with more uniform grid mesh and better aesthetical shape, the stability behavior of form-finding lattice shell is also improved compared to traditional single-layer spherical lattice shell. Aimed at solving the problem of complicated member types of form-finding lattice shell, a optimizing method based on graphing is presented, which could not only increases the load capacity, but also decreases member types at the same time.Chapter 4 explores the design ideas of free-form lattice shells. The design process of free-form lattice shells is as follows:at first, form-finding of free-form surface is accomplished by applying force density method, aimed at looking for a surface that could not only fulfill the aesthetic requirement but also transfer loads fluently in structural view; then using the point clouds acquisition, NURBS curve construction and NURBS surface construction technologys that widely used in reverse engineering to construct a continuous surface; the normal automatic mesh method adopted in softwares is not suitable for free-form structures, a new mesh method combined with artificial control and local auto mesh is presented, another optimizing step based on force density method is taken after rough grid mesh, then a fluent and aesthetic grid mesh could be gained through these processes. The number 1 sun valley of Expo Axis is taken as an example to investigate the form-finding and grid mesh of free-form lattice shells according to the design ideas. The static and stability behavior of form-finding sun valley lattice shell and practical sun valley lattice shell will be compared at last.Chapter 5 investigates the effect of member buckling on overall stability of lattice shells systematically. In stability analysis, a method is presented to introduce initial imperfection in members to lead members to buckling, imperfection amplitude is determined by comparison of FEM results and calculation according to steel structure design code. The analyzing method considering only node imperfection is proper if there is no member buckle before overall buckling; while for lattice shells that members buckle before overall buckling, member imperfection is more detrimental than node imperfection on stability capacity, and stability analysis without member imperfection will overestimate the load capacity of the structure. For the above, a reasonable calculation procedure for stability analysis of lattice shells is proposed. The stability analysis of sun valley describes the buckling process of members and their effect on overall stability.Chapter 6 investigates the stability bearing capacity of shuttle-shape lattice columns considering the action of bending moment through geometrically and materially nonlinear FE method. The emphasis is on the effects of orientation and distribution pattern of initial geometric imperfections on the stability bearing capacity of shuttle-shape columns. The character of moment stiffness and shear stiffness of shuttle-shape columns is summarized. Attention is paid on how to adjust parameters to get proper proportion of moment stiffness and shear stiffness to maximize stability bearing capacity of shuttle-shape columns. A practical computing method to calculate the stability bearing capacity of shuttle-shape lattice columns considering the action of bending moment is proposed, which could be used quickly by designers.The last chapter gives the summary and points out some future research topics of single-layer lattice shells.