WHAT IS FOOTING. VARIOUS TYPES OF FOOTING. OBJECTIVES OF FOOTING

FOOTING:-

Definition:-

Footings are structural members used to support  columns and walls and to transmit and distribute their loads to the soil in such a way that the load  bearing capacity of the soil is not exceeded,  excessive settlement, differential settlement,or  rotation are prevented  and adequate safety  against overturning or sliding is maintained.

TYPES OF FOOTING:-

There are three main types of foundation

1. Strip footing

2. Raft/Mat footing
3.Isolated/Pad footing

1. STRIP FOOTING:-
     A Continuous Strip of concrete under a continuous wall carrying a uniformly distributed load

Footing spread is usually  provided:-
1. To facilitate bricklayer a "working space" for building the lower courses of wall
2. To provide "Stability" to the load bearing walls before it is tie down by floors and roof
3. To provide "working space" for the hand excavation in deeper trench excavation

1. WIDE STRIP FOOTING:-
(i) Use in a situation where the load bearing capacity of the soil is low (ex. soft clay silt made ground)
(ii) Site which may be subjected to "unequal settlement" (Mining areas) or where the subsoil is "not uniform" in character

2. INVERTED "T" BEAM STRIP FOOTING:-
     Use in a Situation where there is a danger of the foundation failing as a beam in the longitudinal direction

3. DEEP STRIP FOOTING:-
    A deep strip footing is a narrow footing which is used for normal soil and normal loads and is made 0.9 m deep

In a deep, narrow trench Excavation by hand is not possible

Excavation by  mechanical means is  possible

4. STEPPED STRIP FOOTING:-

   A stepped strip foundation  is often used on a sloping  site where the steps allow  the foundation to follow  the slope without too  much excavation, when  compared with excavations  and retaining walls.

2. RAFT/MAT FOOTING:-

     Raft footing is a continuous footing that supports an entire structure, such as a floor also known as foundation mat.

Best suited in the following conditions:-

1. Column loads are extremely heavy thus requiring large bases.

2. Columns are closely spaced in both directions and if pad footings are used, it would overlap and may almost cover the whole building area.

3. Ground bearing capacity is low, such as in compressible soft natural

TYPES OF RAFT/MAT FOOTING:-

Solid Slab Raft:-

   Flat Concrete slabs uniform thickness over whole raft area with pedestals or without pedestals

Beam and Slab Raft Footing:- 

Beam and slab rafts are alternatives to the solid slab raft and are used where poor soils are encountered, have pedestals

Cellular/Framed Raft Footing:-

These type of foundations are used on soft soil such as soft clay or pit.

3. ISOLATED/PAD FOOTING:-

Pad footing is the support used at a point load such as columns or framed structures. They may be circular, square or rectangular and consist of a block or slab of the thickness.

(i) The pad footing may be stepped if they are required to spread the load from a heavy column. The pads are usually shallow but deep ones can be found depending on the structure.

(ii) Isolated or independent slab of concrete foundation to support concrete columns or steel pillars, detached brick or masonry piers

(iii) The pier or column bearing on the center point of the slab

Types of Pad Footing:- 

Combined Footings:- It is used where the bearing area of closely spaced columns overlapped

Cantilever Footings:-

It is design to accommodate eccentric loads