Foundation and Columns ans its Load

Foundation and it's Types

Foundation

Foundation is the lowest portion of a structure which transfer the load into the supporting soil. The main purpose of the foundation is to distribute the total weight of the superstructure over a large area of soil.

Types of Foundation

Types of foundation are classified in to two general categories;

1. Shallow Foundation
2. Deep Foundation

Shallow Foundation

It is the type of foundation in which the foundation is situated instantly below the lowest part of a structure. The depth of foundation is equal or less than it's width. Shallow foundation also consist of  different classification.

       Classification of Shallow Foundation

1. Spread Footing
2. Combine Footing
3. Mat and Raft Foundation

1 Spread Footing

  Spread Footing consist of a wide base of foundation for transmitting the load to the soil over a wider area.

2 Combine Footing

  Combine Footing consist of a common footing provided to two column which may be  either rectangular or trapezoidal.

3 Mat and Raft Foundation

  Mat and raft foundation consist of dense reinforced concrete slab which covers the total bottom soil wit low bearing capacity where structural loads are heavy.

Deep Foundation

A deep foundation in which the foundation is placed at a deeper depth below the ground level. The depth of foundation much greater than it's width. It is also classified in different classification.

        Classification of Deep Foundation

1. Pile foundation
2. Cofferdam
3. Caisson Foundation

1 Pile foundation

   Pile foundation is a type of foundation where a slender member of wood or concrete or steel is inserted into the ground for transferring the load of a structure. The load is transferred stronger stratum by friction.Pile foundation classified in different categories based on function and material.

Classification based on function 

1. Bearing piles
2. Friction piles
3. Sheet piles
4. Anchor piles
5. Batter piles
6. Fender piles
7. Compaction piles

Classification based on Material

1. Timber piles
2. Concrete piles
3. Steel piles

2 Cofferdam

    A cofferdam is a temporary structure which excludes the water from a given site to ovoid the construction on a dry structure.

       Classification of Cofferdam

It is classified in six different categories.

1. Earth cofferdam
2. Rock fill cofferdam
3. Single cofferdam
4. Double cofferdam
5. Crib
6. Cellular

Caisson foundation

Caisson foundation is a watertight structure made of wood, steel or reinforced concrete which excavate for the excavation for the foundation of bridges, piers etc.

    Types of caisson

1. Open caisson
2. Pneumatic caisson
3. Box caisson

How we find the depth of Foundation and Beam

Depth of Foundation

Basics

  Density of dry soil = 25 to 35 KN/cubic meter

  Internal friction of soil = (θ) =20 degree

  Density of wet soil = 15 to 25 KN/cubic meter

  Internal friction of soil = (θ) = 19.2 degree

According to Rankin Formula

       D = P (1-Sin(θ))²

           W (1+Sin(θ))²
where,
   D = Depth of foundation
   P = Total load on foundation or structure
  W = Unit weight of soil or Density of soil
 (θ) = Angle of repose or Internal friction of soil

Example
\Load of structure 55 KN/m²
Density of soil = 16 KN/m
Angle of repose = 20

       D = P (1-Sin(θ))²

           W (1+Sin(θ))²

      D = 55 (1-Sin 20)²
          16 (1-Sin 20)²

     D = 0.82 m

How we find depth of Beam by Thumb rule

We can find the depth of beam by Thumbs rule. In this rule the depth of the beam in foots is equal to the length of beam in inches.

For example

   the length of beam = 15 ft

\  the depth of beam = 15"

If it is in Meters then the length will multiply by 3.28 . For example the length of beam is 10 m then first of all we convert it in to the ft.

10 x 3.28 = 32.8 ft

The depth of beam = 32.8"

Column and it's Types

Column

Rcc columns is a vertical structural member which takes complete load of the beam , slab and the entire structure and transfer loads directly  to the underneath soil . That means the whole entire columns of building are stand on the earth.

Types of Columns

      There are several types of  of columns.

1. Rectangular columns/Square columns
2. L- Type of column
3. Y  Type of column
4. Short column
5. Long column
6. Circular column
7. I- Type column

Steps of construction of columns

 There are four steps of construction of columns

1. Columns layout work
2. Column reinforcement work
3. Column form work
4. Poring of concrete

Types of columns

1 Square/Rectangular Column

https://daecivilinfo.blogspot.com/2020/06/columns.html

Most of the building structure was constructed by square or rectangular column. Significantly both are having same components and it is differ based on its architect view.

These type of column was economically good and easy to do shuttering, placing reinforcement & Concrete.

2 L- Type column

The L type column has used in boundary wall construction and heavy type L column was used in the turning of metro rail or bridges construction.

3 Y -Type column

These type of column mostly using for bridges construction.

The design of bridges to sustain the dead load of the structure & live load of the vehicle motion, the load was eventually distributed to the column.

4 Short column

If the ratio effective length of the column to the least lateral dimension is less than 12, the column is called as the short column. A short column fails by crushing (pure compression failure).

5 Long column

If the ratio effective length of the column to the least lateral dimension exceeds 12, it is called as long column. A long column fails by bending or buckling.

6 Circular column

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  Circular columns are symmetric about any centroid axis. If you compare a square column with circular column having same diameter as the side of the square column, circular column has a similar cross section area but larger second area.

7 T - Type column

  It is utilized based on design requirement of a structure. T shape columns are widely use in construction of bridges.

Steps of construction of columns

Column layout work

       It is the first step of column construction. Layout proceed by surveying instruments. In this step the location of column is marked practically in field.

Column reinforcement work 

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               When marking of column is done the reinforcement of columns are placed according to the drawing.

Checklist on site 

1. Check the number and diameter of vertical bars
2. Check the spacing between the vertical bars
3. Lapping in alternate bars should come at same height
4. Lapping should not come inside beam or slab
5. Lapping should be at L and 2L of column as per structural notes.                         3         3
6. The spacing between stirrups is as per the drawing
7. The hook should be bend properly at right angle
8. Check the stirrups corner . vertical bars should come at right angle edge of stirrups properly bond with binding wire. 

Column Formwork

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 Column carry the load of structure and hence they are critical . It is the most important to align them for vertically so that the load is transmitted properly

   Guideline for column Formwork

1. To hold the concrete shuttering or formwork firmly in place and for proper alignment a concrete pad called starter is cast before fixing the formwork
2. Column box or shuttering for columns is made of plywood sheets or steel sheets fabricators with adequate stiffeners
3. The thin firms of oil or grease should applied to the inner surface of shuttering to easily remove from a column. After the concrete harden shuttering should be properly to it's vertically and diagonals to be checked to ensure accuracy in dimensions.
4. Formwork has to be thoroughly supported with props size before pouring the concrete. so  that it does not moves horizontally or vertically during concreting.
5.  Gaps in shuttering joints should be sealed with plaster or a piece of wood to prevent any leakage of slurry.
6. Appropriate space is to be provided in the inner face of the shutters and reinforcement by fixing cover black of about 40 mm.
7. Shuttering should be removed after 24 hours. If it is need to be removed earlier, it should not be removed within 16 hours.
8. The removal of shutters has to be done gently without jerk so that edges of columns are not damaged.

   Concrete Pouring

                           Concreting of column is done in two different methods.

1. Manually
2. By using machine or pump

  Guideline followed during and after concreting

1. Use machine mix concrete for less amount of concrete and ready-mix concrete for large amount of concrete.
2. Approval of placing concrete whether by manually or by pump should to be taken from the client.
3. Concrete should be poured up to slab bottom and the remaining column should be concreted during beam and slab concreting.
4. Mechanical vibrator must be used for full compaction of the column, but remember excess vibration can create segregation of the concrete.
5. The target slump is 160 mm.
6. Concrete should not be poured from more than 1.5 m height.
7. Always avoid construction joints in the columns.
8. Covers should be given properly as per the structural drawings.
9. During concreting pouring, the temperature should be below 30 C.
10. Check vertically horizontally of the column after pouring and vibrating the concrete.