What Is Footing?
Footing is one of the most important parts of a structure which transfers loads of a structure to the underlying soil. The selection of suitable types of footing generally depends on the following factors:
1. The depth of the soil at which safe-bearing strata exists.
2. The type and condition of soil.
3. The type of superstructure.
Types Of Footing:
The different types of footing used for building construction are described below:
- Wall footing/Strip footing.
- Spread Footings
- Isolated footings.
- Stepped footings.
- Combined footings.
- Sloped footings.
- Mat or Raft foundation.
- Strapped footings
- Pile foundation.
1. Strip footing:
This type of footing is commonly used as foundations of load-bearing walls where the soil is of good bearing capacity.
2. Spread Footing:
As the name suggests, a spread is given under the base of the foundation so that the load of the structure is distributed on wide area of the soil in such a way that the safe bearing capacity of soil is not exceeded.
3. Isolated Footings:
These types of footings may be square, circular, or individually rectangular slab of uniform thickness, provided under each column.
4. Stepped Footings:
The main purpose of using stepped footing is to keep the metal columns away from direct contact with soil to save them from corrosive effects. This type of footing is used to carry the load of metal columns and transmit this load to the below ground.
5. Combined Footings:
When two or more columns are supported by a footing it is called combined footing. This type of footing may be rectangular or trapezoidal in plan. Combined footing is provided under the following situations.
• When columns are close to each other and their individual footings overlap.
• Soil having low bearing capacity and requires more area under individual footing.
• The column end is situated near the property line and the footing can not be extended.
6. Strap Footing:
In this type of footing, the outer and inner column is connected by a strap beam, does not transfer any load to the soil.
The individual footing areas of the columns are so arranged that the C.G of the combined loads of the two columns passes through the C.G of the two footing areas.
Once this criterion is achieved, the pressure distribution below each individual footing will be uniform.
7. Raft Foundation:
This foundation covers the entire area under the structure. This foundation has only RCC slab covering the whole area or slab and beam together.
These types of footing are adopted when heavy structures are to be constructed on soft made-up ground or marshy sites with uncertain behavior. Raft foundation is also known as mat foundation.
8. Sloped Footing Or Trapezoidal Footing:
These types of footing having a sloping top or side faces are known as sloped footings. They are useful in the construction of formwork.