The bolted ball joint of the grid structure is solid, but the part connected with the rod will be reserved for hollowing out when the factory is processed. The bars of the grid generally have an open web section, such as round steel pipes, square steel pipes, etc., and rolled steel, cold-formed thin-walled steel, etc. can also be used.

The deadweight calculation of the grid includes two parts: the deadweight of the rods and the deadweight of the nodes. The weight of the nodes of the grid generally accounts for 15%-25% of the total weight of the grid members. Most of the rods of the grid are made of steel, and the bulk density of steel is generally 78.5kn/m3. Generally, its self-weight is calculated by computer, but the self-weight per unit area of the grid can be estimated first. The self-weight of the double-layer grid can be estimated by the following formula: g0=a*(qw**0.5)*l/200 , Among them, a-factor, when steel pipe is used as the member, take 1.0; when steel is used, take 1.2; qw-the standard value of roof load or floor load except the weight of the grid; l-the short span of the grid .