What Is Combined Footing?
When two-column lie on the same row or at the common footing, then this type of footing is known as combined footing. In combined footing, two columns are so close to each other.
When The Combined Footing Is Used?
The combined footing is used in some special situations. Here is the list of these situations:
1- When the footing of two-column is close to each other then in this type of situation we use combined footing.
2- If the load-bearing capacity of the soil is low and there is a requirement for more area under the individual footing, in such conditions we use combined footing.
3- If a column is situated near the boundary line and it is not possible to project its footing within the boundary line, then in such type of condition we use combined footing.
Types Of Combined Footing
A combined footing is mainly four types and here are the lists of these combined footing:
- Rectangular combined footing
- Trapezoidal combined footing
- Raft combined footing
- Strap combined footing
Rectangular Combined Footing
When the two or more columns in a row have one footing and the shape of the footing is rectangular, then this type of footing is called rectangular combined footing.
The rectangular combined footing is provided in such a situation where the projection of footing is not possible within the boundary line.
Trapezoidal Combined Footing
When a combined footing is constructed in the shape of trapezoidal, then this type of footing is known as trapezoidal combined footing.
In the combined footing when the load of one column is greater than the other, then in this type of situation the trapezoidal combined footing is provided.
The main work of trapezoidal combined footing is transferring the non-uniform load of building to the soil.
Raft Combined Footing
The raft combined footing is used when there is a need to increase the bearing power of the soil.
Raft combined footing is very useful when a load of the building comes uniformly on the soil.
The raft combined footing prevents the tendency of the collapse of the building by increasing the bearing power of the soil.
The raft is designed in such a way that the allowable bearing power of the soil is not exceeded.
Strap Combined Footing
Strap combined footing is a type of combined footing in which there are two or more column footing is connected to each other by a strap beam (concrete beam).
Here the work of the strap beam is to prevent the footing from overturning by connecting the footing to each other by using a concrete beam called a strap beam.
Advantages Of Combined Footing
Using the combined footing in the construction of a building gives a lot of advantages. Here is the list of advantages of using combined footing:
1- The main advantage of combined footing is, it increases the load-bearing of soil ( increases the strength of soil to hold the heavy building).
2- The second advantage of combined footing is, it prevents the footing from overturning by connecting the footing to each other using a strap beam.
3- The third advantage of the combined footing is, it helps to make the centers of gravity of the column load and center of gravity of soil reaction remain in the same vertical line.
4- The fourth advantage of combined footing is, if there is no space to spread the footing near the boundary line then in this type of situation the combined footing is used.
5- The fifth advantage of combined footing is, it helps to get the uniform load distribution under the footing.
Disadvantage Of Combined Footing
Here are the lists of disadvantages of combined footing:
1- The main disadvantage of using combined footing is the groundwater level rises.
2- The second disadvantage of combined footing is the shape and the size of these footing is varying due to the condition.
3- The third disadvantage of combined footing is it reduces the footing area because for more than one column we use only on footing.
Frequently Asked Questions (FAQ)
In what conditions the combined footing is suitable?
A combined footing is suitable in three conditions. The first condition is when the two-column are very close to each other, the second condition is when the load-bearing capacity of soil is low and the last condition is if there is no space for the construction of the last footing near the boundary line.
What is a strap combined footing?
The strap combined footing is a combination of spread footing having two columns connected through the concrete beam.
In how many shapes do be constructed a combined footing?
A combined footing is constructed in the square, t-shape, or trapezoidal shapes.
What is a strap beam in the strap combined footing?
A strap beam is a concrete beam and its work is to connect the nearby footing.
What are the different types of combined footing?
A combined footing is mainly four types first one is Rectangular Combined Footing, the second one is Trapezoidal Combined Footing, the third one is Raft Combined Footing, the last one is Strap Combined Footing.
What are the advantages of combined footing?
The main advantage of using combined footing is it increases the load-bearing capacity of the soil, prevents the footing from overturning, etc.