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Isolated footing is defined as the footing, which is provided beneath the column to distribute the loads safely to the bed soil. This kind of footing is used to support single-columns and when the columns are arranged relatively at long distance. This the most inexpensive kind of footing.
Types of Isolated footing:
(i) Pad footing
(ii) Stepped footing
(iii) Sloped footing
Shapes of Isolated footing:
(i) Square footing
(ii) Rectangular footing
(iii) Circular footing.
Show the types and shape of isolated footings in the below Figure.
In the square footing, reinforcement are provided to resist the bending moment and shear force at the critical sections. The code suggests giving the reinforcement in similar manner along both the directions. The difference in effective depth values among the two directions is only minor and it can be neglected.
Rectangular footing:
The rectangular footing should have the reinforcement bars in the longer direction, to efficiently transfer the loads in similar manner to that of shorter direction. In the longer direction of the footing, some part of the total reinforcement placed in the short direction is placed in the middle portion. This portion is referred as band width and the length equal to smaller side of the footing.
Advantages of Isolated footing:
(i) Isolated Footing is cost effective.
(ii) Construction is easy.
(iii) Material used is concrete.
(iv) Does not require skilled labors for construction.
Disadvantages of Isolated footing:
(i) It will have settlement.
(ii) It has limited capacity.
(iii) It can be subjected to torsion or tension forces easily.
Note :- Respected readers! Circular columns are often used in domestic and commercial construction due to their aesthetic value. And their footings are mostly designed in circular shape.Below is a spreadsheet for design of circular footings as per American Concrete Institute,Building Code Requirements 318-02 available for free download.
1. Input Data & Design Summary
2. Analysis
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