- Raft foundations are used for combining the footings of a group of columns of a building when columns carry heavy loads on weak soils.
- Also, when the isolated footings occupy more than 75% of the plan area, raft foundations are used.
- Centers of gravity of column loads and the footing are matched to obtain uniform upward soil pressure. If this is not possible, non-uniform pressures should be taken into account in design.
- The exact manual analysis of raft foundation is not possible because the beams run in both the directions and the share of the loads by these beams cannot be easily calculated.
- In raft foundation, the settlements under individual columns tend to be uniform.
- Therefore in conventional design, the reactions in the beams at their junction with the columns are so adjusted that their sum equals to the column loads.
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