First, the structure form
Large-span structure according to the geometric shape, combination, structure, material and mechanical characteristics of different can be divided into flat structure system and the spatial structure system two kinds big.
Plane structure: beam (truss and truss), plane rigid frame and arch structure.
Space structure: plate truss structure, shell structure, most of the suspension structure, cable-stayed structure, tension structure etc.
Second, in the form of grid
In accordance with the truss chord layers can be divided into double grid and three layer grid. Three layer steel increase grid height and reducing chord force, reducing the grid size and the ventral rod length, when the truss span large triple layer space trusses steel quantity to reduce, but increase of members and joints, is more complex.
1 The grid is a space trusses, bar arrangement must ensure there are no combination of variability. Must meet the following conditions
2 The commonly used form of double grid:
2.1, plane trussed lattice grids: upper and lower chords correspond exactly and and the web member in the same vertical plane, the vertical compression diagonal rod tension. (two to two orthogonal space truss, orthogonal diagonal grid to grid, three)
2.2, four cones system network frame: composed of several inversion four cones according to certain rules. (is put four pyramid grids, are put to four pyramid frame, board type four pyramid grids, oblique put four pyramid grids, star four pyramid frame)
2.1, plane trussed lattice grids: upper and lower chords correspond exactly and and the web member in the same vertical plane, the vertical compression diagonal rod tension. (two to two orthogonal space truss, orthogonal diagonal grid to grid, three)
3 The selection of Grid: grid selection should be combined with the engineering plane shape, architectural requirements, load and span size, support and cost factor comprehensive analysis. According to "Specification for design and construction of grid structure" (JGJ 7-91) Division: large span is more than 60m; in a span of 30-60m; the small span below 30m.
3.1 latticed truss structure: the space truss supporting way of peripheral supporting, points, the surrounding supporting and supporting, on both sides and trilateral bearing, etc
The 3.2 grid height and grid size: the height of the net and the roof load, span, plane shape, support conditions and equipment pipeline and other factors.
Immunity requirements and roof drainage slope 3.3 grid: allow immunity shall not exceed the following values, as -L2/250 -L2/300.L2 is used as the roof; the floor truss to the short span. Roof drainage is generally 3%-5%.
Third, rack the calculation of the point
Network frame structure design to meet the industry standard "network frame structure design and construction regulations"（JGJ 7-91）Requirements.
1 Direct effect and indirect effect, space truss structure to use phase loads of internal force and displacement calculation, and should be according to the specific situation of earthquake effect, temperature change, such as indirect support settlement and construction installation load caused by the internal force and displacement is calculated.
2 The internal force analysis method of space truss truss structure: external load according to static equivalent principle, effect of load nodes in the area concentrated in the slave node. Analysis of the internal force of the structure is to ignore the influence of joint stiffness, assuming the hinged rods bear axial force. When the internode load, should also consider the bending effect. The internal force and displacement of truss structure can be calculated according to the elastic stage. According to the grid type, according to the provisions of the span size (space truss displacement method, cross beam differential method, the method of sandwich plate, illusion moment method)
Fourth, the space bar system finite element method (fem)
Space bar system finite element method (fem) is also called the space truss displacement method, analysis with the rack bar as the basic unit, to the node displacement of the basic unknown quantity. A bar to establish the relationship between internal force and node displacement element stiffness matrix, and then according to the balance of each node and change coordination condition to establish relationship between node load and displacement of structure, form structure stiffness matrix and the total stiffness equation.
Basic assumptions: 1, rack hinged for the space of node and link only bear axial force. 2, structural material is perfectly elastic, network frame deformation under load is small, in line with the small deformation theory.
The finite element method calculation steps:
1, according to the space truss structure, load symmetry selection calculation diagram, and the node and bar code to reduce the total stiffness matrix bandwidth, node Numbers should follow the principle of minimum good difference of adjacent nodes
2, calculate the element length and the rod and the whole axis angle cosine
3, the primary cross-sectional area of each bar
 4, the establishment of stiffness matrix; local and global coordinates unit
5, set the total stiffness matrix, reduced matrix capacity
6, the establishment of dynamic load identification
7, the introduction of the boundary conditions on the total stiffness of
8, to solve the total stiffness equation, the displacement of each node value
9, according to the node displacement bar internal force calculation
10, according to the internal forces of rod adjustment section member, and re calculation, no more than 4-5
Fifth, the design of truss structure.
The truss member can be used in the steel, hot-rolled steel and cold-formed steel
Sixth, node design
Node common form: 1, welded hollow spherical joints
2, the bolt ball node 3, node 4, welding steel plate welded steel pipe node and link 5 direct tandem node
Grid nodes constructed to meet the following requirements; 1, reasonable force, definite force transmission 2, to ensure rods intersect in a point, does not produce additional moment 3, simple structure, convenient manufacture and installation, consumption quantity of Steel 4 small, avoid difficult to check, cleaning, painting and easy retention of moisture or dust dead, tube type interface at both ends closed.
Seventh, shell
In accordance with the shell layer is divided into single-layer reticulated shell and double layer reticulated shell. According to the surface shape classification is the spherical shell, cylindrical shell, hyperboloid latticed flat shell and twisted reticulated shell, single block, torsional reticulated shell of hyperbolic paraboloid shell and cutting or combined to form a curved surface latticed shell structure.
Bearing shell structure must ensure that the calculation model of geometric structure in arbitrary vertical and horizontal load constant and various requirements on the supporting condition of the shell.
Reticulated shell structure should be calculated under the action of the external load internal force and displacement calculation and necessary stability, and should be according to the specific circumstances of earthquake, temperature and support settlement and construction and installation under the action of load internal force, displacement, stability calculation. Meet the "technical specification" requirements of the 61 JGJ  shell structure.
Shell is a quasi flexible high-order statically indeterminate structure, geometric nonlinearity is generally obvious structure, the overall stability of geometry structure change is also very sensitive, the shell is calculated mainly by the geometrical nonlinear finite element method. The hinged connection of double-layer latticed shell, single-layer shell joints should be used in rigid or coplanar node unit normal stiffness is zero, which belongs to the variable geometry.
Eighth, suspension structure
In accordance with the cable force characteristics, the suspension structure is divided into: single suspension system, prestressed dual cable system, prestressed saddle shaped cable net and Transverse Prestress stiffening monolayer cable system, prestressed cable arch and a tensile structure, suspension shell piece of tensile structure, cable membrane structure and mixed structure in the form of a hanging.
Suspension structure design principles: suspension structure respectively for the use and construction stage were external loads, the prestressing effect of internal force and displacement calculation, and under the action of earthquake and the temperature variation of internal force and displacement is calculated according to the specific circumstances.