What are the common classifications of space frames?
I. Classification by surface form (the most intuitive and core classification)
This is the primary classification that determines the appearance and basic mechanical properties of the space frame.
1. Flat Space Frame
Features: All members are located within one or more parallel planes, and the shape is flat.
Stress: A two-way stressed spatial plate structure, mainly bearing vertical loads.
Advantages: Relatively simple design, manufacturing, and construction; suitable for various planar shapes (rectangular, circular, polygonal).
Applications: Large industrial plants, warehouses, waiting halls, multi-functional sports venues (roofs covering the competition hall).
2. Curved Space Frame (Space Shell)
Features: Members form one or more curved surfaces, with a clear spatial shape.
Advantages: Better mechanical performance, allowing for larger spans with less material; rich and aesthetically pleasing architectural forms.
Common types:
a. Cylindrical space shell: Unidirectional curved surface, like a cylindrical shell. Commonly used in train station platforms and aircraft hangars.
b. Spherical space shell (dome): Double-curved spherical surface. It is the most classic and efficient form of space shell, suitable for gymnasiums, planetariums, and theaters.
c. Hyperbolic paraboloid space shell (saddle-shaped surface): The shape is dynamic and has good drainage performance.
d. Free-form surface space shell: Derived from complex architectural forms, a product of modern parametric design, with the highest technical difficulty.
II. Classification by grid composition (determines the internal member layout)
This is the most core classification in flat space frames, directly affecting stress performance and steel consumption.
1. Cross Truss System
Composed of intersecting planar trusses.
2. Two-way orthogonal/oblique: Trusses intersect vertically or obliquely, suitable for rectangular planes.
3. Three-way intersection: Composed of planar trusses intersecting at 60°. More uniform stress distribution, good rigidity, suitable for large-span circular and triangular planes.
4. Four-sided pyramid system
The basic unit is an inverted four-sided pyramid. This is currently the most widely used and technically mature flat space frame system.
a. Orthogonal four-sided pyramid: The four sides of the pyramid base are parallel to the building boundaries. High rigidity, uniform stress distribution, and fewer types of members. b. Inclined Quadrangular Pyramid: The four sides of the pyramid base are at a 45° angle to the building boundary. This results in a more rational force distribution and saves on steel, but the boundary treatment is slightly more complex.
c. Hollowed-out Quadrangular Pyramid/Star-shaped Quadrangular Pyramid: Some members are removed from the basic form to create a richer grid, suitable for medium spans to save on materials.
5. Triangular Pyramid System
The basic unit is a triangular pyramid. It offers greater structural height, maximum spatial rigidity, and optimal load-bearing performance, making it suitable for large spans or complex layouts, but the node construction is more complex.
III. Classification by Number of Structural Layers
1. Double-layer Space Frame: The absolute mainstream. Composed of an upper chord layer, a lower chord layer, and an intermediate web member layer. It has a wide economic span range (30m-120m).
2. Triple-layer Space Frame: Adds an intermediate chord layer. Suitable for ultra-large spans (>100m) or heavy loads, significantly improving stability and reducing grid size, but the node construction is complex.
3. Single-layer Space Shell: No web members; the curved surface is formed by a single-layer grid. It has a light and aesthetically pleasing appearance, but requires extremely high stability and rigid node connections, and is often used for small to medium spans.
IV. Classification by Connection Node Type (Affects manufacturing and installation)
1. Bolted Ball Joint Space Frame: The nodes are steel balls connected by high-strength bolts. It has the highest degree of prefabrication, the fastest installation, and a simple appearance. It is the mainstream for flat space frames.
2. Welded Ball Joint Space Frame: The nodes are hollow steel balls, and the members are welded to the balls on-site. It has high load-bearing capacity and strong adaptability, suitable for large spans, heavy loads, and complex curved space shell structures.
3. Intersecting Node (Direct Steel Pipe Intersection Welding) Space Frame: The members are directly cut and welded at their intersections, eliminating the need for ball joints. It has a smooth appearance and saves on steel, but requires extremely high precision in cutting and welding. Often used in large tubular truss structures.
V. Classification by Material Used
1. Steel Space Frame: The absolute mainstream, using carbon structural steel or low-alloy high-strength steel. 2. Aluminum alloy space frame: Extremely lightweight, corrosion-resistant, and aesthetically pleasing, suitable for locations with special requirements regarding weight, corrosion resistance, or architectural appearance (such as swimming pools, aquariums, and entrance canopies of landmark buildings), but the cost is high.
