What is a space frame?
A space frame is a light, three-dimensional truss structure made up of straight struts that meet at nodes. In Dutch it is also called ruimtevakwerk. Whereas an ordinary truss works in a single plane, the struts of a space frame form a spatial grid of triangles and pyramids. This allows the structure to carry loads in several directions and makes large spans possible without intermediate supports.
How it works
- Triangles. A triangle is rigid: the struts are mainly loaded in tension or compression and hardly in bending. This makes slender struts possible.
- Double-layer grid. The most common form has a top and a bottom grid, connected by diagonals. The whole behaves like a thick but very light slab.
- Nodes. The struts (usually steel or aluminium tubes) are connected with steel ball nodes with threaded holes, with plates or by welding. The well-known German MERO system uses spherical nodes.
- Two-way load transfer. Because the forces are spread over the whole grid, a space frame is also relatively insensitive to the failure of a single strut.
Application
Space frames are found in halls, exhibition centres, stations, petrol stations, canopies and atria. Points to watch:
- Structural engineer required. A space frame is always designed by a structural engineer; strut forces and node details are decisive.
- Supports. The bearing points must be able to take the reactions, including horizontal movement due to temperature. Sliding or hinged bearings are often used.
- Corrosion and fire. Steel struts and nodes must be galvanised or coated. Where fire requirements apply, extra protection is needed, because slender struts heat up quickly.
- Roof covering. The roof is usually laid on the top grid, on purlins or directly on the nodes; make sure there is a fall for drainage.
Common mistake: hanging heavy services or signage from an arbitrary strut afterwards. Struts are designed for axial forces; a point load in the middle of a strut causes bending it was not designed for.
Related terms
- Truss
- Span
- Dome
- Steel
- Structural steel sections
- Mechanical stress
- Roof truss
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