Double layer grid is a term for civil engineering published in 2003. The double-layer grid is a spatial structure composed of upper chord, lower chord and web rods, and is the most commonly used form of grid. The commonly used forms of double-layer grids are as follows: plane truss system grids (two-way orthogonal vertical grids, two-way orthogonal diagonal grids, three-way grids): quadrangular vertebra system grids (positive To the quadrangular pyramid grid, evacuating the quadrangular pyramid grid, star-shaped quadrangular pyramid grid): triangular pyramid system grid.

Plane truss system grid




The plane truss system grid is generally as follows:

Two-way orthogonal forward grid

The grid itself is a geometrically variable system. It is suitable for the situation where the building plane is square or close to square and the span is small. The internal force of the rods in the two directions has little difference, and the force is more uniform. It is composed of two groups of plane trusses parallel to the boundary at 90° crossing each other. The length of each plane truss in the same direction is the same.

Two-way orthogonal diagonal placement and diagonal diagonal placement grid

The short truss has an embedded effect on the long truss, and the force is favorable. The corners produce pulling force, often in the form of no corners. The space rigidity is larger than that of the orthogonal orthographic grid, the force is even, and the steel is saved. It is suitable for the situation where the building plan is rectangular.

Three-way grid

Geometrically invariant system, the space rigidity of the grid is large, the force performance is good, and the internal force distribution is relatively uniform. The number of rods is large and the node structure is more complicated. The three-way grid is suitable for large spans and the building plane is triangle, hexagon, polygon and circle.


Quadrilateral system grid

The inverted quadrangular pyramid is the constituent unit of the quadrangular pyramid system grid. The grids in the upper and lower chord planes of this kind of grid are all square. The centroid of the upper mesh is the intersection of the lower mesh. From the four intersections of the upper chord grid to the lower chord intersections are connected with oblique web rods to form an inverted quadrangular pyramid unit. The connection mode of each independent quadrangular pyramid can be that the base of the quadrangular pyramid is connected to the base, or the corners of the base of the quadrangular pyramid are connected to the corners.
The inverted quadrangular pyramid is the constituent unit of the quadrangular pyramid system grid. The grids in the upper and lower chord planes of this kind of grid are all square. The centroid of the upper mesh is the intersection of the lower mesh. From the four intersections of the upper chord grid to the lower chord intersections are connected with oblique web rods to form an inverted quadrangular pyramid unit.
The connection mode of each independent quadrangular pyramid can be that the base of the quadrangular pyramid is connected to the base, or the corners of the base of the quadrangular pyramid are connected to the corners.

Triangular cone system grid

Triangular cone grid

Structural features: The basic unit is a geometrically invariant system, with good overall torsion and bending rigidity and relatively uniform force.

Applicability: Suitable for peripheral supporting grids with circular and polygonal planar shapes, side-length ratios greater than 1.5, and large-span projects.

Evacuate the triangular cone grid

Structural features: The internal force of the lower chord is increased and the uniformity is slightly worse, and the rigidity is worse than that of the triangular pyramid grid.

Applicability: It is suitable for peripheral support grids with circular and hexagonal planar shapes, and the side length ratio is greater than 1.5.

Honeycomb triangular cone grid

Structural features: This kind of net frame has a short upper chord under pressure and a long lower chord under tension, which can give full play to the role of the cross-section of the members, with reasonable force and lower stiffness than the triangular pyramid net frame.

Applicability: Suitable for peripheral support grids with circular and hexagonal planar shapes, medium and small spans.