Types Of Footings & Foundations
Advantages & Disadvantages of Continuous wall footing
Advantages of Continuous wall footing
1). Easy to built.
2). It does not require skilled labors & expensive tools to construct this types of footing.
Disadvantages of Continuous wall footing
i). Durability is less when compared with other types of footing.
2). Spread Footing
For the distribution of the total structure load on a wide area of soil A spread is given under the base of the foundation in such a manner that the safe bearing capacity of soil is not exceeded. It is also an important types Of Footings.
3). Isolated Footing
This type of footing supports of individual column that’s why it is called as isolated footing. It is square, circular or individuals rectangular slab of uniform thickness, provided under each column.
If good soil is available then these kind of footings are economical. The isolated footing essentially consist of a bottom slab. Generally this type of footing used when the bearing capacity of soil is high. Loads on footings are less and columns of a building are not closely spaced. This types Of Footings. can be of three types:-
i). Simple footing.
ii). Sloped Footing.
iii). Stepped footing.
i). Simple Footing
Simple footing is also called as pad footing, flat footing & plain footing which are provided under each column independently. This type of footings can be square, circular or rectangular.
To keep the metal column safe and away from the direct contact with soil to save them from corrosive effects steeped footing is adopted.
This type of footing constructed in olden days. Now they are outdated.
iii). Sloped Foundation
The strapped footing having sloping top or side faces are known as sloped footings. This type of footing is useful in the construction of form work. It is also used in high rise building when the structural load is high. Sloped footing are also known as trapezoidal footings. This is also an important types Of Footings.
i). The concrete quantity required to construct trapezoidal footing is less hence we can save the cost of concrete and steel while constructed to this type of footing.
4). Combined Footing
When two or more column are supported by a footing it is called combined footing. This footing may be of rectangular or trapezoidal shape.
When columns are closely spaced and in this scenario when we try to construct individual footings then footings of these two columns will overlap. So, in this case it is better to provide combined footing than isolated footing.
When one column is closed to property line the center of gravity of column will not coincide with footing. In such cases it is necessary to provide combined footing with that of adjacent internal column.
To achieve this the center of gravity of footing area should coincides with the center of gravity of total loads as two or more columns. Combined footings are further classified into following types based on their shapes.
i). Rectangular combined footing
The rectangular combined footing is provided when one of the projection of the footing is restricted or the width of footing is restricted.
The Trapezoidal Combined is important Types Of Footings . This footing is provided when load of one column is much more than the load of other column
iii). Strap beam Combined Footing
Strapped beam type Combined Footing is used when one column is located on a property line, resulting in on eccentric load on portion of footing, therefore in this type of footing a beam is provided to the adjacent column of the footing to restrain the overturning effects. it is also an important Types Of Footing.
When Combine footing is provided?
Combine footing is provided under following situations :-
i). When columns are close to each other and their individual footing overlap.
When columns are very near to each other so their footings overlap.
ii). Soil having low bearing capacity and requires more area under individual footing.
iii). The column end is situated near the property line and the footing can not be extended.
When the end column is near property, So that is footing can not spread in that direction.
5 ). Mat or Raft foundation
The raft footing is also called as mat footing. If load transfer by columns in a structure are heavy and allowable soil pressure is small than footing require more area. So, in order to spread the load over large area with less depth we have to increase the footing area and in this case if we planned to go with individual footing then footing will overlap with each other.So, to avoid this a common footing is provided which supports all columns.
Such kind of footing is called as raft footing. Raft footing is the combine footing that covers entire area under a structure & supports all the columns. This is also an important types Of Footings.
Raft footing is used to support
i). Storage equipment, silos, cooling towers, storage tanks, chimneys, various industrial structures & building with basements. Where continuous water proofing is needed.
This foundation covers the entire area under the structures. This foundation has only R C C Slab covering the whole area of slab and beam together. Raft foundation is adopted when heavy structures are to be constructed on soft made up ground or marshy sites with uncertain behavior. This is also an important types Of Footings.
Advantages and disadvantages of Raft foundation
Advantages of Raft foundation
i). Site access restricted. Mobilization of heavy equipment not possible.
ii). To control the settlement within the IS code limit.
iii). Higher settlements values in design, Avoids unequal settlement.
iv). Can be customized as per soil conditions and consumer requirement economy.
v). Very fast & easy compared to open individual foundation.
Disadvantages of Raft foundation
i). When the loads are high and soil bearing capacity is low , the design optimization becomes difficult. Make design more expensive.
ii). Required for raft foundation that what we requires than individual footings.
iii). When size of raft trends to increase beyond some limits designer prefer deep foundation like pile is a better option.
2). Deep Foundation
i). Pile foundation
Pile foundation is the long cylinder column made of steel and reinforced concrete or sometimes timber to support the structure & transfer the loads at desire depth either by end bearing or friction pile.
It is mostly used in bridge construction where the soil has poor strength. This is also an important types Of Footings.
Pile foundation is used in following condition:-
i). When the soil is very weak and when the groundwater table is high.
ii). When there is presence of expensive soil or black cotton soil.
iii). When structure is subjected to uplifting forces.
iv). When there is soil erosion.
2). Caissons Foundation
In this type of foundation a Pre–fabricated hollow box or cylinder is jump into the ground to some desired depth and then filled with concrete to form a foundation. Caisson foundation is most open used in construction of bridge pier & other structures that require foundation beneath river and other bodies of water. This is also an important types Of Footings.
Where we provides shallow or deep foundation
Shallow Foundation are constructed where soil layers at shallow depth is able to support the structural loads. The depth of shallow foundations are generally less than its width. This is also an important types Of Footings.
Deep foundation are employed where the soil immediately below the structure within reasonable depth is not capable of supporting the load of building.
Hence the structure has to be rested on a strata at a greater depth. The function of deep foundation is to transmit the load of the building to firm layers deep inside the ground.
layers at shallow depth is able to support the structural loads. The depth of shallow foundations are generally less than its width. This is also an important types Of Footings.
So, these are the Types Of Footings
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