The domestic grid structure is mainly divided into two types: welded spherical joint grid and bolted spherical joint grid. The bolted spherical joint grid has a large amount of processing in the factory and is convenient for on-site installation. It is suitable for special-shaped structures with tight on-site construction periods, restricted construction conditions and power consumption, complex grid shapes and difficult positioning of rods. It is widely used in large stadiums, exhibition centers, theaters, shopping malls, terminal buildings, waiting halls, factory workshops, warehouses, TV towers, etc. This article focuses on the bolted ball joint grid.

1. Decomposition of design drawings

A complete bolted ball joint grid design drawing should include design instructions, grid plan, grid upper and lower chords and web bar layout, support and support details, member material table, bolt ball material table, bolts, Sleeve, jacking wire material table, sealing plate, cone head material table, detailed drawing of bolt ball processing (additional if there are other requirements, such as hanging parts, ventilation room, etc.). First, check the grid plan and foundation plan provided in the drawing to ensure that the position of the grid support is consistent with the foundation. Then check the bar material table provided by the grid diagram, mainly check the axis length of the grid, then check the welding length of the bar according to the axis length, and then check the blanking length of the bar. After everything is correct, the workshop bar blanking table can be drawn according to the bar material table.

Second, the calculation of members

The length of the rod of the bolt ball net frame is controlled by the diameter of the bolt ball, the cutting amount of the bolt ball, the length of the sleeve, the length of the cone head and other factors.
The formula for calculating the length of the rod is:
Bar blanking length = bar welding length-2 (cone length-cone spigot length-1mm).
(In the formula, 1mm is the gap between the steel pipe and the cone to ensure the welding quality)
The length of the rod after welding = (the geometric length of the rod)—(the radius of one segment of the ball + the radius of the other segment of the ball + the length of one segment of the sleeve + the length of the other segment of the sleeve) + (cutting amount of one segment of bolt ball) + (cutting amount of another segment of bolt ball ).

3. Grid support design

Bolt ball grid support is generally Q235 steel, while the bolt ball is 45 steel. Due to the large difference in material between the two, the support installation on the construction site generally adopts the form of bolt connection, and the support bolts generally use M20 ordinary bolts. . The support processing and installation methods can be divided into two. The first support is that the support bolts and the support are welded together, and the support is screwed into the bolt ball by rotating the support during construction. The support plate must be round; the second support is that the support bolt and the support are not welded. And open a hole on the top of the supporting plate, and use a casing wrench to screw the supporting bolt into the bolt ball.

4. Matters needing attention in rod processing
 
Due to the welding shrinkage of the steel pipe and the cone (sealing plate) during the welding process, the blanking length of the rod should be added to the welding shrinkage when drawing the rod processing material table. The welding shrinkage value can be calculated according to the formula or according to the workshop According to the actual measured data, the latter is generally adopted in actual operation.

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