Reinforcement, construction and main reasons to use raft foundation
The main reasons why the designer choose matt/raft foundation instead of single footings:
2- When high loads are applied (such like multi story buildings) with poor soil bearing as well.
3- In the case of private structures such as (towers, chimneys, and water tanks).
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Raft foundation reinforcement:
Raft foundation reinforced with two lower and upper steel mesh. The main steel reinforcement is in the long direction, because the moments are greater in the long direction.Additional reinforcement:
* Additional reinforcement is in placed at the maximum negative moments.* Bottom mesh of steel reinforcement is placed at the columns bottom.
* Additional steel reinforcement is placed at midspan.
Permissible places to overlap reinforcing steel
* Bottom steel connections and overlaps are permissible in the middle of the span between columns.* The upper steel connections are permissible at the columns.
* The length of development length is according to the code 60D, where D is the diameter of the reinforcement used.
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Raft foundation steps of construction:
- Excavation works at the required levels.
- Pouring the normal concrete under the raft foundation.
- Formwork of the raft foundation sides.
- A cover is placed in concrete spacers with a thickness of 7.5 cm in the form of strings every meter.
- Reinforcement works according to the plans, which forms two steel meshes (a lower steel mesh and upper steel mesh) with steel chairs to carry the upper mesh with a diameter not less than the iron used in the two meshes.
- Columns and walls are made with the upper mesh, and the length of the overlap is not less than 60D or 1 meter, whichever is greater.
- It's recommended to put steel marks of the thickness of the raft foundation required for concrete pouring.
- Pour concrete with the required thickness.
- Concrete must hydrated by with water for a period of 7 days, which starts 24 hours from the concrete pouring.
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