Bolt Ball or Welding Ball?

    Design Code Basis

    JGT 10-2009 Steel grid bolt ball joints

    JGT11-2009_Steel grid welded hollow ball joints

    Bolt Ball Joints Application

    Bolted ball joints are mainly used in grid and reticulated shell structures, they are composed of steel balls, high-strength bolts and sleeves, fastening screws, cone heads (sealing plates) and other components.

    The bolted ball joint grid is suitable for the roof structure with small span, light roof weight and simple building function. 

    For the roof with a span of more than 45m, the roof adopts reinforced concrete slabs and other heavy roofs, or the roofs of buildings with high importance and dense personnel such as airports, stations, and exhibition centers, welded ball joint grids should be used.

    Bolt ball joints are not thin-walled joints, and their diameter should not exceed 300mm; the commonly used maximum bolt  specification is M64.

    Welding Ball joints Applicaiton

    Welded hollow sphere joints are mainly used in grid truss and reticulated shell structures, and can also be applied in multi-bar intersection joints and support joints in tube truss structures.

    1. When welded ball joints are used for double-layer or multi-layer grids or reticulated shells, they should be calculated as hinge joints; when used for single-layer reticulated shells, they should be calculated as rigid joints; when used for plane or space trusses, they should be calculated as rigid joints calculate.

    2. When the outer diameter of the ball is greater than 300mm, ribs can be added inside the hollow ball to increase the bearing capacity of the joint; when the outer diameter of the ball is greater than or equal to 500mm, one-way or cross ribs should be added inside the ball. The ribs should be arranged in the axial plane of the rod with large axial force, and its thickness should not be less than the thickness of the ball wall.

    3. The minimum included angle of the rod connected to the welded hollow spherical joint should not be less than 30°, and the clear distance between adjacent rods should not be less than 10mm. When the stress of the rod is small, the clear distance can be taken as 0.

    4. The connection between the steel pipe rod and the hollow ball should be equipped with an inner liner. If the wall thickness is greater than or equal to 6mm, a bevel should be provided, and if the wall thickness is less than 6mm, the bevel may not be provided.

    5. Avoid using large balls for small tubes.

    Let's hear advantages and disadvantages from ChatGPT

    Q: What are the advantages and disadvantages of bolted ball joints and welded ball joints in the grid structure?

    ChatGPT answers:

    Advantages of grid structure bolted ball joints:

    1. It is easy to install and disassemble, and can quickly assemble and disassemble the structure;

    2. The node does not need to be preprocessed, it can be used directly;

    3. It can be assembled on site, suitable for occasions that require quick installation and disassembly;

    4. Can be reused.

    Disadvantages of bolted ball joints of grid structure:

    1. Since the connection method is bolt connection, the installation accuracy requirements for the nodes are relatively high, and the operation must be strictly in accordance with the design requirements;

    2. Since the connection of the nodes may become loose, regular inspection and maintenance are required.

    Advantages of Welding Ball Nodes:

    1. The connection is stable and will not loosen;

    2. It can withstand large force and has high structural stability;

    3. The node connection is more beautiful, no need to use bolts and other connecting parts, and the structure is more concise.

    Disadvantages of Welding Ball Nodes:

    1. Welding requires professional skills and has high requirements for welding techniques and workers;

    2. If the structure needs to be changed or disassembled, it needs to be cut and re-welded, which is not easy to disassemble and reuse;

    3. Heat treatment is required, and the operation time is longer.