FOUNDATION AND FOOTING
DIFFERENCE BETWEEN FOUNDATION AND FOOTING
First of all, the structure or part which helps to transmit the load from upper stories through column up to the ground is actually called as footing.
Every column in the structure have to have a footing supported on firm and hard strata. As there may be many numbers of columns, so can be footings !
These overall arrangement of footings are interconnected with beams and all which ultimately distributes the loads safely to the ground, can b called as a foundation.
WHY FOUNDATION & FOOTINGS ARE REQUIRED
1 To distribute the weight of the structure over large area so as to avoid over-loading of the soil beneath.
2 To load the sub-stratum evenly and thus prevent unequal settlement.
3 To take the structure deep into the ground and thus increase its stability, preventing overloading.
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ISOLATED FOOTING
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.
AREA OF APPLICATION
Commonly used for shallow foundations in order to carry and spread concentrated loads, caused for example by columns or pillars.
Isolated footings can consist either of reinforced or non-reinforced material. For the non-reinforced footing however, the height of the footing has to be bigger in order to provide the necessary spreading of load.
Should only be used when it is absolutely certain, that no varying settlements will occur under the entire building. Spread footings are unsuitable for the bearing of widespread loads. In this case, either strip (continuous)
WALL FOOTINGS
wall footing or strip footing is a continuous strip of concrete that serves to spread the weight of a load-bearing wall across an area of soil.It is the component of a shallow foundation.
AREA OF APPLICATION
The wall footing can be constructed from stone, brick, plain concrete, or reinforced concrete. Economical wall footing can be constructed provided that the imposed load needed to be transmitted are of small magnitude and the underlying soil layer is of dense sand and gravels.
Therefore, wall footing is best suited for small buildings.
COMBINED FOOTING
A strap footing is a component of a building's foundation. It is a type of combined footing, consisting of two or more column footings connected by a concrete beam.
AREA OF APPLICATION
The distance between two columns is small and when soil bearing capacity of soil is lower and their footings overlap with each other.
When one column is close to a property line or sewer pipe, the center of gravity of column will not coincide with footing. In such cases, it is necessary to provide combined this footing with that of the adjacent internal column.
STRAP /CANTILEVER FOOTINGS
Strap footing consists of two or more individual footings connected by a beam called a strap. It is also sometimes called a cantilever footing.
AREA OF APPLICATION
- When the foundation, not sufficient area to transfer the loads safely to the round. Such as in case of footing build on the property line.
- It also useful when the soil supporting the foundation does not have enough bearing capacity to transfer the load safely and the area of the footing cannot be increased beyond the limit.
- When the new structure built near the existing building or structure. And the existing building cannot support the loads from the new structure. Then a new column and footing have to provide her the existing structure. But there will limit space or footing
MAT / RAFT FOUNDATION
According to the Dictionary of Earth Sciences, Raft foundation, a type of foundation, used for heavy loading, or construction on soft ground, composed of a continuous slab of reinforced concrete below the entire surface. In Venice, many of the medieval raft foundations
underneath the large churches are made of wood.
AREA OF APPLICATION
Raft foundations may be used for buildings on compressible ground such as very soft clay, alluvial deposits and compressible fill material where strip, pad or pile foundations would not provide a stable foundation without excessive excavation. The reinforced concrete raft is designed to transmit the whole load of the building from the raft to the ground where the small spread loads will cause little if any appreciable settlement.
PILE FOUNDATION
Pile foundation, a substructure in which piles are used to transfer a load from a structure to the soil. Pile foundations are particularly appropriate when the building or structure is to be erected on soil that is not stable or is saturated with water.
AREA OF APPLICATION
It is used
• When stratum of required bearing capacity is at greater depth.
• Where the soil is compressible. • Where the soil is water-logged.
• Where the soil is of made-up type.
EXAMPLES :
• Foundation of heavy bridges, high-rise buildings
• Water front installations (pier, wharf, docks etc.)
CAISSON FOUNDATION
A caisson foundation also called as pier foundation is a watertight retaining structure used as a bridge pier, in the construction of a concrete dam, or for the repair of ships. It is a prefabricated hollow box or cylinder sunk into the ground to some desired depth and then filled with concrete thus forming a foundation.
Caisson foundations are similar in form to pile foundations, but are installed using a different method. It is used when soil of adequate bearing strength is found below surface layers of weak materials such as fill or peat. It is a form of deep foundation which are constructed above ground level, then sunk to the required level by excavating or dredging material from within the caisson.
AREA OF APPLICATION
The foundation system of and the soils beneath the building prevent the complex from moving vertically. When a load is placed on soil, most soils settle. This creates a problem when the building settles but the utilities do not.
Caisson foundation is Most often used in the construction of bridge piers & other structures that require foundation beneath rivers & other bodies of water. This is because caissons can be floated to the job site and sunk into place.
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