What is camber?
Camber is a deliberate upward curve built into a beam, floor or roof to offset all or part of the deflection that occurs under load. It is expressed as the distance between the highest point at midspan and the straight line between the two supports. A cambered member looks slightly arched when unloaded and becomes flatter under its own weight and the imposed load. In Dutch the term is zeeg or toog.
Why use camber?
Every beam deflects under load, and in timber and concrete the deflection increases further over time because of creep. Without camber this can lead to:
- visibly sagging floors or roof edges;
- ponding on flat roofs, because the fall to the outlets is lost;
- cracks in walls and finishes that rest on the beam.
Application
- Steel beams: the fabricator bends the camber into the section. This is common for long spans in industrial halls.
- Concrete floors: precast lattice girder slabs are propped to a camber during installation. Prestressed units gain an upward camber from the prestressing itself.
- Timber beams: glulam beams can be manufactured with camber.
- Flat roofs: cambered main beams help to maintain the fall towards the outlets.
The camber required depends on the span, material, section and load. It is often quoted as a fraction of the span, for example span/400, but the correct value comes from the structural engineer’s calculations.
Points to watch
- Do not guess: too little camber leaves the deflection visible, too much results in a permanently arched floor. Follow the structural drawings.
- Check the orientation: always install a cambered beam with the curve facing up.
- Connections: allow for movement between the unloaded and loaded state where walls and window frames sit below a beam.
Related terms
- Toog
- Beam
- Span
- Flat roof
- Rolled steel beam
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