A grid structure is a type of architectural form composed of supports, members, ball joints, and protective systems. It is one of the rapidly developing and widely used types within spatial grid structures. Unlike the hierarchical relationship between components in a planar structural system, a grid structure is either formed by a single continuous spatial body or expanded by many members. Each component is part of the overall structure, distributing loads according to the spatial geometric characteristics, with simple force transmission and good overall structural integrity. Therefore, it can achieve large spans with smaller cross-sections, reducing the structure's self-weight and improving overall economic efficiency.

Decoding Four Key Aspects of Detailed Design in Steel Truss Engineering Structures

1. Base Node Deepened Design

Foundation Node Deepened Modeling

The grid structures are typically placed on the tops of columns, beams, and other lower supporting structures. The support nodes refer to the grid nodes on the supporting structure. The in-depth design of the grid starts with the support nodes, as their elevation and position determine whether the grid construction can proceed normally.

Points to note for deepening the support node:

The requirements for the elevation and placement of embedded parts on the top surface of the concrete or steel structure must be precise.

The support node form needs to be determined; common types include rubber flat support and basin-type support. Attention should be paid to the constraint direction of the support.

The edge support nodes are often close to the parapet wall, and attention must be paid to the clear distance between the support nodes and the parapet wall, generally maintaining a distance of 50mm or more.

The intermediate support carries a heavy load, often requiring a larger base plate size. Attention must be given to whether the cross-section of the lower concrete or steel column meets the requirements; if not, the column head joint must be expanded.

The tensioned truss bearing structure requires attention to the potential collision between the rod elements at the support location with the lower supporting structure. A review is necessary. The distance from the bottom of the ball joint at the support to the bottom plate of the support should meet the requirement of not colliding with the inclined web members or the connecting beams.

Retainage measures must be implemented on the outer side of the grid support.

Web Frame Engineering

2 Ball Node Deepened Design

Bolted Ball Node Model

Welded Ball Node Model

The grid ball nodes are divided into two types: welded balls and bolted balls. Bolted balls are secured with high-strength bolts, while welded balls are connected through on-site weld seams.

Key points to note during the in-depth design of the ball node include:

Bolt ball node accessories vary among different manufacturers, and component data should be obtained prior to deepening.

The materials for the steel ball, high-strength bolts, sleeve, set screw, cone head, or cover plate in the bolt ball joint should comply with design and specification requirements.

High-strength bolts in bolt ball joints should be selected according to specifications.

The diameter of the bolt ball should ensure that adjacent bolts do not touch within the ball and meet the requirements of the sleeve contact surface.

The cone heads or covers at the ends of the rod members in bolt ball joints are connected by welding. The bearing capacity of the weld joints should not be less than that of the connected steel pipes; the cross-sectional area of the cone heads and the thickness of the covers should both be calculated and determined based on the actual load.

Welded spheres are typically hollow spheres formed by welding two hemispheres together, and it is necessary to determine whether to set reinforcing ribs based on the magnitude of the load.

The outer diameter to wall thickness ratio of the welding ball, the ratio of the ball outer diameter to the main pipe outer diameter, and the ratio of the ball wall thickness to the main pipe wall thickness must meet the specifications: the ratio of the ball outer diameter to the wall thickness should be between 25~45, the ratio of the ball outer diameter to the main pipe outer diameter should be between 2.4~3.0, the ratio of the ball wall thickness to the main pipe wall thickness should be between 1.5~2.0, and the ball wall thickness should not be less than 4mm.

Welding balls to steel pipes should employ bevel groove welds, and a gap should be left between the steel pipe and the ball to ensure that the weld penetrates fully, achieving equal strength to the steel pipe.

When the number of ball joint connecting rods is excessive, some rods may intersect to reduce the ball diameter; however, they must comply with the structural requirements specified by the regulations: the axes of all intersecting rods must pass through the centerline of the ball; when two rods intersect, the rod with the larger cross-sectional area must be fully welded to the ball (if the cross-sectional areas of the two rods are equal, the tensile rod is chosen), and the other rod must be bevel-welded to the intersecting rod, but it should ensure that 3/4 of the cross-section is welded to the ball, and stiffeners should be set as required; for rods under high stress, support plates can be set as needed.