Introduction of bolt ball joint in grid structure

       Introduction of bolt ball joint in grid structure: the bolt ball joint of steel grid structure is solid, but the part connected with the member will be reserved and hollowed during the factory processing. Generally, the hollow section of the members of the grid structure is the best, such as round steel pipe, square steel pipe, rolling section steel, cold-formed thin-walled section steel, etc.  
       The self weight calculation of grid structure includes two parts: member self weight and node self weight. The dead weight of the nodes of the grid generally accounts for 15% - 25% of the total weight of the grid members. Most of the members of the grid structure are made of steel, and the volume weight of general steel is 78.5kn/m3. Generally, its self weight is calculated by computer, but the self weight of the grid per unit area can be estimated roughly first. The self weight of the double-layer grid can be estimated by the following formula: G0 = a * (QW * * 0.5) * L / 200, where, A-coefficient, when the member adopts steel pipe, takes 1.0; when the profile steel is ad、

opted, takes 1.2; QW - standard value of roof load or floor load except the self weight of the grid; l-short span of the grid.
       The bolt ball joint of grid structure shall be composed of bolt, steel ball, pin (or screw), sleeve, cone head or sealing plate and other parts (Figure 4.4.1), which is suitable for connecting steel pipe members. The steel pipe, sealing plate, cone head and sleeve of the bolt ball joint should be No.3 Steel specified in the national standard carbon structural steel GB700-88 or 16Mn steel specified in the national standard technical conditions for low alloy structural steel gb1591-88, the steel ball should be No.45 steel specified in the national standard, and the bolt, pin or screw should be No.45 steel specified in the national standard technical conditions for alloy structural steel gb3077-8845. The product quality shall be in accordance with the provisions of jgj75.1-91, the industrial standard bolt ball joint of steel grid.
       The diameter of bolt ball can be determined according to the following formula: in order to meet the requirements of sleeve simple contact surface, the following formula should be used for Accounting: D - diameter of steel ball (mm); θ - Minimum included angle between two bolts (RAD); D1, D2 - diameter of bolt (mm), D1 > D2; ξ - ratio of length of bolt into steel ball and bolt diameter; η - ratio of sleeve circumcircle diameter and bolt diameter. The ξ and η values shall be determined according to the design values of bolt tension and pressure respectively, and the values can be taken as ξ = 1.1, η = 1.8. The diameter of the steel ball shall be the larger of the two calculation results.
       The high-strength bolts of grid structure shall adopt the performance grade of 8.8s or 10.9s specified in the national standard gb1228-91 high strength large hexagon head bolts for steel structure, and conform to the provisions of the national standard gb196-81 coarse tooth common thread. The design value of tensile bearing capacity of each high-strength bolt shall be calculated according to the following formula: where -- design value of tensile force of high-strength bolt (n); ψ -- influence coefficient of bolt diameter on bearing capacity when bolt diameter is less than 30m m, ψ = 1.0; when bolt diameter is greater than or equal to 30mm, ψ = 00.93; -- design value of tensile strength of high-strength bolt after heat treatment; 430n / m ㎡ for 40Cr steel, 40b steel and 20mntjb steel, 365n / m ㎡ for 45 steel; α eff -- high The effective section area of the strength bolt (m ㎡), which can be selected according to table 4.4.4. When the bolt is drilled with a pin hole or keyway, α eff shall take the smaller value of the thread or the keyway of the pin hole.
The diameter of the connecting bolt of the compression member can be appropriately reduced according to the bolt diameter obtained from its internal force, but it is necessary to ensure that the sleeve has sufficient compressive strength. The sleeve shall be calculated according to the bearing pressure, and the bearing pressure of the effective section at the notch and end shall be checked.