There are different types of foundation based on no. of a factor. The isolated footing is one of the most popular and simplest types of foundation used worldwide. Foundations are very important to the building. Ultimately the entire load of the building is transferred to ground through the foundation.
Isolated footings are most commonly used footings for Reinforced cement concrete column because it is simple and most economical. An isolated footing is used to support a single column. Isolated footings are independent footings which are provided for each column.
This type of footing is used when
1- Columns are not closely spaced.
2- Loads on footings are less.
3- The Safe bearing capacity of the soil is generally high.
The Design of Isolated Footing
The Objective of the Design of Isolated Footings is to Determine:
1- Area of footing
2- Thickness of footing
3- Reinforcement Details of footing with a satisfying moment and shear force consideration.
4- Check for development length and shearing stresses.
All these things carried out with considering the loads on footings, Safe bearing capacity (SBC) of the soil, Grade of concrete and Steel. Minimum cover to main reinforcement shall not be less than 50mm on the surface of the contact with the earth face. The diameter of main reinforcement shall not be less than 10mm.
The Design Steps followed in the Design of Footings are
1- Find out an area of footings based on factored loads.
2- Assume suitable thickness of the footing
3- Find out the critical section for flexure and shear
4- Find out bending moment and shear forces at the critical section
5- Check the adequacy of the assumed thickness
6- Find out reinforcement detail
7- Check for bearing stresses
8- Check for development length
Isolated Footing Design Example
1- Column = 14” x 14”
2- Steel grade= fy=60 Ksi
3- fc’ = 3 ksi ( for footing)
4- fc’ = 4 ksi ( for column)
5- sL.L =260 kips
6- sD.L = 390 kips
7- bearing capacity = qa = 6 ksf 5’ below the grade
Watch this video step by step