In this article, we will discuss
What is Footing | What is Spread Footing | 7 Types of Spread Footing | Reasons to Use Spread Footings | The Formula for Calculating Spread Footing Area
 |
| Spread-Footing in Foundation |
What is Footing
The weight of a building is transferred to the ground by the footing, which is made up of columns, walls, and lateral loads from earth-retaining structures.In designing a building's foundation, the size and weight of the building as well as the type of soil it is built on are very important. To make sure a structure is strong, it is important to look at how soil pressure is distributed. Spread footing is an important structural part that gives a building's foundation strength.
What is Spread Footing/Pad Footing?
The spread footing is used to support the column and walls, as well as to move and distribute the weight of the building to the ground below it.
When loads are applied in the upward direction, this footing acts like an inverted cantilever. This type of footing is usually a rigid part, and the symmetric footing is the only case where they are orthogonal.
This type of footing can be a round, square, or rectangular slab of the same thickness. Sometimes it is stepped to spread the load over a larger area.
Spread footing has a base that is a little bit wider than a load-bearing foundation base. This type of foundation is also called a "stepped spread."
During this type of footing, an RCC member is used to make a base foundation. This wider bottom spreads the weight over a larger area, making the building more stable.
The spread footings are made of concrete and steel, and their design makes it less likely that they will fail than other spot footers.
What is another name of Spread Footing?
This kind of foundation is also called a pad foundation. In this kind of foundation, the bottom is wider than the top so that the weight of the building can be spread out over a large area.- This kind of foundation is good for walls and columns made of stone.
- After digging the trenches to the right depth, these foundations are put in place.
- For a maximum depth of 3 m, it is a good deal.
When it comes to wall footings, the projections only go in one direction, but when it comes to columns, they go in both.
7 Types of Spread Footing
- Footing for a wall.
- Column Footing or Isolated Footing
- Combined Footing.
- Cantilever Footing or Strap Footing
- Constant Footing.
- Footing with an Inverted Arch.
- Footing for grillage.
- Raft Foundation or the Mat Foundation.
Read More
1. Footing for a wall
A wall footing, also known as a strip footing, is a continuous strip of concrete used to distribute the weight of a load-bearing wall across an area of soil. It is part of a shallow foundation. Wall footings carrying direct vertical loads can be designed in either plain or reinforced concrete.Wall footings are frequently either simple or steep. Wall footings are further classified into two types:
- Simple wall footing.
- Stepped wall footing.
2. Column Footing or Isolated Footing
In isolated column footings, each column has its own footing.So that the weight of the columns is spread evenly and safely over the ground, the size of the footing is kept the same no matter how big the area is. Most of the time, this kind of footing is built on top of a 100 or 150-mm concrete bed.
Design engineers figure out how thick the footing needs to be and if it needs to be reinforced.
The thickness of the footing can be the same or it can change.
For a single column, this type of footing is used. This kind of footing is further broken down into three types:
- Stepped footing.
- Simple spread footing.
- Sloped footing.
3. Combined Footing
When a single footing needs to hold two or, in rare cases, more than two columns, it is called a "combined footing." When two or three columns are close to each other, we give them a single substructure, which is called a "combined footing."When there are two or more columns in a row, this kind of footing is used. There are two types of footing in this:
- Combined footing in the shape of a rectangle. Columns are uniform or identical.
- Combined footing in the shape of a trapezoid. Columns aren't all the same and don't have the same amount of space.
4. Cantilever Footing or Strap Footing
A strap footing is part of the foundation of a building. It is a type of combined footing that is made up of two or more column footings connected by a concrete beam. A strap beam is this kind of beam.A combination of two or more individual footings connected by a strap beam is what is known as a strap footing. Cantilever footing or pump handle foundation are two other names that are occasionally used to refer to it.
5. Constant Footing
A footing that is considered to be continuous is one that is capable of supporting more than two columns. A comparison can be made between this footing and the strip footing used for walls. The loads that are carried by each individual column are either transferred directly to the footing slab or when the loads are substantial, they are transferred via a longitudinal beam that runs in the longitudinal direction.This type of foundation is appropriate for use in earthquake-prone areas and also helps prevent differential settlement.
6. Footing with an Inverted Arch
An inverted arch or invert is a type of civil engineering structure that looks like an arch that has been turned upside down. In the simplest case, the arches just spread the downward loads of the viaduct piers over a larger area of ground, just like an inverted arch bridge does.This type of foundation is used in places where the soil is very weak, the building's weight is concentrated on the walls, and deep excavations are not possible.
Read More
7. Raft Foundation or the Mat Foundation
A raft foundation, which is also called a mat foundation, is basically a slab that rests on the ground and goes all the way around the building. This supports the building and puts its weight on the ground.
A Raft foundation is actually a single footing that goes all the way around the bottom of a building and holds up all the walls and columns.
In this type of foundation, an R.C.C. slab with or without a beam of the right thickness is used.
Reasons to Use Spread Footings
- Its purpose is to support a building's base, which may be a single foundation or multiple piers.
- Adds Stability
- Lessen uneven building settlement
- It acts as a load-bearing component between the upper level and the foundation.
The formula for Calculating Spread Footing Area
The bottom area of the spread footing can be determined by using the formula that is presented below:A=Qt/q
Where,The total load that is going to be applied to the spread footing is equal to Qt, where q is the base area of the spread footing.
Advantages of Pad Footing
When the spread footing is used as a building's foundation, there are a number of benefits, such as:- The spread footing spreads the weight of the structure over a large area of soil below it. This makes the structure more stable.
- Compared to other types of footing, spread footing doesn't have much or any chance of failing.
- This kind of footing makes buildings last longer because it keeps damage from happening inside.
- These footings are used to give structure support all the time.
- These footings are easy to put in building structures and make it easy to build basements.
- Compared to a load-bearing foundation, a variety footing foundation has a wider bottom. The wider bottom spreads the weight of the structure over a larger area, making the structure more stable.
- This type of footing is mostly made of concrete and steel that has been strengthened.
- Most of the time, these footings are used in building homes.
- Lessens the cracking caused by the ground moving.
- Stabilizes the ground around the base of the building.
- Construction, design, and internal control costs can all be cut.
- Differentiates in size and quantity
Disadvantages of Pad Footing
- Not good for all types of soil.
- You have to fill up the whole lot at once, but making that much concrete on your own is a lot of work.
- Pouring concrete is a lot of work, so you can't do it by yourself.
Spread/Pad Footing Design
- First, we need to figure out the sizes and loads of the different parts of the structure at the foundation level.
- Then we need to gather information and set the foundation for the plan.
- After that, we figure out how deep and where the footing element is.
- We also need to find out how much weight the soil can hold.
- Next, we figure out the total and local settlement, as well as the strength of the concrete.
- Then we choose the type of steel, the size of the footing, and the thickness.
- After this step, we plan the connection between the substructure and the superstructure.
- Lastly, we make sure that the uplift and stability against sliding conditions are good.
FAQ's
1. What is the difference between spread footing and continuous footing?
1. The spread footing is used to support the column and walls, as well as to move and distribute the weight of the building to the ground below it.2. Continuous footing is footing that supports more than two columns on a wall. When the individual column is placed on the strip footing, the load from the column is transferred to the footing slab, which helps create stability for the foundation
2. Which type of footing is best?
If the loads that a structure's columns have to carry are heavy and the soil pressure that can be put on it is low, then the footings need more space. In this case, it might be better to put the same footing under all the walls and columns. Raft Footing is the name for this kind of footing.3. Which grade is best for foundation?
M25 Grade ConcreteWhen pouring foundations, M25 is frequently used as a foundation concrete mix (footings). It is also an excellent choice for domestic slab foundations for house and bungalow floors.