What is Combined Footing ?
When the soil under the foundation does not have ample strength to bear the load of the structure, then footings are provided. The function of the footing is to act as the supporting agent of the foundation. It also protects the foundation from settling down beyond the permissible limit.
Combined footing is basically a combination of various footings, which utilizes the properties of different footing in a single footing based on the requirement of the structure. It carries two or more columns along a straight line.
The reasons for providing combined footings are as below.
- It is necessary to provide the combined footing in case of overlapping, when two columns are close enough to each other.
- They are provided where the load bearing capacity of the soil is low, and it will go below the optimum limit.
- It is required to provide combined footing in the structure, when the resultant loading is close enough to the column of the building.
Depending on the shape of the combined footing, there are three types of combined footing, namely, rectangular, trapezoidal and T-shaped combined footing.
Consider the below figure for different types of combined footing :-
To ensure the uniform distribution of pressure below the combined footing, the centroid of the footing must coincide with the centroid of the column or structure supported by the combined footing.
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1. Design of Combined Footing 1
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