A continuous support is a support condition in which a beam or floor does not terminate over the bearing point, but extends past it to the next span. This contrasts with a simply supported beam, which hinges at each support. A continuous support belongs to continuous structures and provides a more favourable force distribution.
Difference from simple supports
The structural difference shows in the bending moment distribution:
- Simply supported — moments at supports are zero; the maximum moment is at midspan
- Continuous — a negative support moment arises over the intermediate support; the midspan moment is reduced
A continuous beam is therefore stiffer and deflects less. Especially in two or more spans, this leads to significant material savings.
Structural characteristics
When designing a continuous support, several aspects matter:
- Top reinforcement — in reinforced concrete, extra steel is needed at the top above the support to take tension
- Bending stiffness — the whole beam contributes to load carrying
- Settlement sensitivity — if an intermediate support sinks, large stresses develop
- Shear force — maximum at the support
Applications
Continuous supports occur in:
- Concrete floors — wide-slab or hollow-core floors spanning over multiple beams
- Steel beams — an HEA beam running over several columns
- Bridges — multi-span bridge decks
- Timber framing — a continuous ridge beam or purlin
Points to consider
- Ensure proper restraint — otherwise the beam still behaves as simply supported
- Allow for moment redistribution — under uneven loading, moments shift
- Detail top reinforcement — sufficient length on either side of the support
Related terms
- Support
- Deflection
- Top reinforcement
- Fixity
- Bending strength
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