Components, systems and materials › Building components › Isolated footing
Isolated footing
What it is
An isolated footing is a pad of reinforced concrete under a single column that spreads the column load over enough soil to keep pressure and settlement within safe limits.
Where it is used
Framed buildings on firm soils with moderate loads and column spacing.
How it works
The column load spreads through the footing to the soil, which pushes back upward. The footing bends like an inverted cantilever from the column face, so main reinforcement is placed near its bottom in both directions.
Types
- Square and rectangular pads
- sloped or stepped footings
- eccentric footings near boundaries, often with strap beams
Materials
Reinforced concrete over a lean concrete blinding layer.
Plan area comes from service load and allowable bearing pressure from the soil investigation. Thickness is decided mainly by punching shear and one-way shear, and reinforcement by bending at the column face. Column bars are anchored into the footing. Cover in contact with soil is larger than for interior members.
Installation and QA steps
- Excavate to founding level and inspect the soil.
- Cast blinding concrete.
- Place reinforcement and column starter bars with spacers.
- Concrete, compact and cure.
- Backfill in compacted layers.
- Footing on loose or filled soil not checked at founding level
- punching failure from insufficient depth
- corrosion from low cover
- differential settlement between footings
Codes cited
- IS 456 (India): Plain and reinforced concrete: general rules for materials, durability, design and construction.
- IS 1904 (India): Design and construction of foundations in soils: general requirements.
Cited by number only. We do not reproduce code text, tables or figures.
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