- Footing are structural elements that transmit to the soil column loads, wall loads or lateral loads. If these loads are to be properly transmitted, footing must be designed to prevent excessive settlement or rotation and to minimize differential settlement.
- To limit settlement within tolerably small amount, it is necessary.
- To transmit the load of the structure to a soil stratum of sufficient strength
- To spread the load over a sufficiently large area of that stratum to minimize bearing pressure.
- If adequate soil is not found immediately below the structure, if becomes necessary to use deep foundations such as piles to transmit the load to deeper, firmer layers.
- If satisfactory soil directly underlies the structure, it is merely necessary to spread load by footings. Such substructure are known as “spread foundation.”
i. Wall Footing
A wall footing is simply a strip of reinforced or plain concrete, wider than the wall that distributes its pressure.
ii. Isolated spread footing under single column
These may be usually square, sometimes rectangular or occasionally circular in plan.
iii. Combined Footing
Supporting two or more column loads. These may be continuous with a rectangular or trapezoidal plan or isolated column footing joined by a beam which is referred to as strap footing.
iv. Mat or Raft Foundation
Which is one large continuous footing supporting all columns of the structure. This is used when the soil is poor.