Foundation | Column Footings | 2021|

 Column Footing

           ➤ Columns are the structure members carrying loads in the Framed structure. The proper design of column footing depends on the load on column, its self weight, bearing capacity of soil stratum, adjoining columns etc.

Foundation are mainly classified as Shallow foundation and Deep foundation

           ➤ Shallow types of foundations are sub-divided into four types.

1. Isolated Footing.
2. Combined Footing.
3. Continuous Footing.
4. Cantilever Footing.

•  Isolated Footing :

➬ a) It is defined as the footing supporting a single isolated column.

     b) The footing is symmetrically placed with column. The increase in the width of footing is obtained by single step or stepped footing or more commonly by sloped or cone-shaped footing.

• Combined Footing : 

1. ⃗  If the two columns of a building are closely spaced, then their isolated footing may overlap.
2. If the loads on the two columns are different in magnitude, then care should be taken to bring the resultant of the two loads at the centroid of the footing plan to avoid bending moments and shear forces in the footing.

• Continuous Footing :

1. Instead a single continuous footing can be provided for all the row columns
2. It provided only when Columns are in a row Instead of individual isolated footing may intermingle.
3. In case of different loads on different columns, the trapezium shape of footing should be selected such that the resultant of column loads lies at the centroid of the footing plan.

• Cantilever Footing :

1. If the exterior or extreme column is very close to the boundary of the plot area, its footing may extend outside the boundary the boundary. So it is not possible to provide its footing directly below it.
2. in such case , strong beam is provided at the bottom connection the exterior column with the base of adjoining interior column.

 ➤ Deep Foundations :

      Deep foundations may be of the following types :

1. Deep strip, rectangular or square footing.
2. pile foundation.
3. Pier foundation or drilled caisson foundation.
4. Well foundation or caissons

• Deep Foundations :

                    As stated earlier, the usual strip, rectangular or square footing come under the category of deep foundation, When the depth of the foundation is more than the width of the footing.

• Pile foundation : 

                       In this Loads are taken to a low level by means of vertical members which may be of timber, concrete or steel.

            Pile foundation transfer the load through friction.

  ➢ Piles used for building foundation may be of four types:

1. Friction pile.
2. End Bearing pile.
3. Combined end bearing and friction pile.
4. Compaction piles.

When pile foundation may be adopted :

1. when pumping of subsoil water would be too costly or timbering to excavations too difficult to permit the construction of normal foundation.
2. Instead of a raft foundation where no firm bearing strata exists at any reasonable depth and the loading is uneven.
3. When a firm bearing strata does exits but at a depth such as to make strip or spread footing uneconomical.

• Pier foundation ( drilled caisson foundation )

                            A pier foundation consists of a cylindrical column of large diameter to support and transfer large superimposed loads to the firm strata below.

          Pier foundation transfer the load only through bearing.

  ➢ Pier foundation may be of the following types :

1. Masonry or concrete pier.
2. Drilled caissons.

• Well foundation ( or caissons ) :

                            Well foundation or caissons are box like structure-circular or rectangular-which are sunk from the surface of either land or water to the desired depth.

               They  are much large in diameter than the pier foundation or drilled caissons. 

   ➣  Caissons foundations are used for major foundation work, such as for:

1. Break waters and other structures for shore protections.
2. Bridge piers and abutments in rivers, lakes, etc.
3. Large water front structure such as pump houses, subjected to heavy vertical and horizontal loads

•  Machine Foundation :

1.  A rigid block of concrete on which the machine is mounted, is own as foundation block.
2. Under the influence of dynamic loads, the foundation block vibrates and causes the underlying soil layer to vibrate.