Types of Concrete foundation

Type of foundation to be used depend on particular use cases. Following are the common types of foundations:

1. Isolated concrete foundation.
These are used under individual columns. They can be square or rectangular in shape.

2. Strip or wall Foundation
These foundations support load from two or more columns. They can be rectangular or trapezoidal in shape. Or two isolated bases joined together by a beam which is known as strap beam or strap footing.

3. Pile Foundations
Pile foundations are used for tall structures or in soil having poor bearing capacity. A group of piles transfer the load of the columns below the soil using friction and sometimes bearing at the end of the piles.

4. Combined Footing
When two columns are closely spaced, if separate isolated footings would overlap, then the columns could be supported on the same footing. If one column is close to a property line or sewer pipe, the load on an isolated base will be eccentric, then it may be economical to combine the footing with an adjacent internal column so that the C.G of the loads on two columns coincides with C.G of the combined footing.

5. Raft or Mat Foundation
When there are a large number of columns, raft foundation or mat foundation can be provided.This is especially necessary with soils having poor bearing capacity, or having differential settlements.It is used when overall loads transmitted by the columns in a structural system are very heavy or Safe bearing capacity of the soil is so small that the individual footings provided would cover more than about one-half of the plinth area of the building.

In the above cases, it is advantageous to support the building on a continuous footing under all columns and walls. Such a footing is called a raft or mat foundation.
Raft foundations are also used to reduce the settlement of structures located above highly compressible deposits.

Factors Effecting Selection of Foundation
1. Bearing capacity of the soil
2. Type of structure
3. Type of loads
4. Permissible differential settlement, and
5. Economy

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