Plane structure system: beam structure (plane truss, space truss), plane rigid frame arch structure.

Space structure system: flat grid structure, reticulated shell structure, most suspended cable structure, cable-stayed structure, tensioned structure, etc

According to the number of layers of the chord, the grid can be divided into two layers three layers. The three-layer steel frame increases the height of the network frame, reduces the internal force of the chord rod, reduces the size of the network frame the length of the belly rod. When the span of the network frame is large, the amount of steel used in the three-layer steel frame decreases, but the increase of the members joints is more complicated.

The frame is a space articulated rod system structure, the rod arrangement ensures no combination variability. W =3j-m- R ≦0

Common forms of double layer grid:

Plane truss system: the upper lower chord are completely corresponding located in the same vertical plane with the ventral chord. (Two-direction orthogonal laying grid, two-direction orthogonal slanting laying grid, three-direction grid)

Quadrangle system grid: composed of several inverted quadrangles according to a certain law. (Positive quadrangle grid, positive quadrangle grid, checkerboard quadrangle grid, oblique quadrangle grid, star quadrangle grid)

Cone grid: the basic unit is an inverted cone whose base is equilateral. (Triangle-cone grid, evacuated triangle-cone grid, honeycomb triangle-cone grid)

Selection of grid structure: the selection of grid structure should be determined based on the comprehensive analysis of the plane shape, building requirements, load span size, support cost of the project.