Cantilever footing is a type of combined footing that the cantilever action is used to balance the eccentricity induced due to the eccentricity of the column load.
The combined action of the eccentric footing (strap footing), strap beam, and inner column foundation, or any structure constructed to rest the strap beam is the combined footing.
Due to the cantilever nation of the strap beam, this type of footings is named cantilever footing.
What is the Canlitlever footing foundation?
- We cannot always construct the column at the center of isolated footing always. When the building is extended to the boundary, footing can not construct in the other land. On these occasions, we have to place the column at the edge of the footing.
- Loading the footing at the edge result in the rotation at the center of the footing or in other words, eccentric loading increases the stress in the soil at the column location.
- It could lead to the settlement of footing or bearing failure of soil when exceeding the allowable bearing capacity. The article on shallow foundation failure could be referred to for more failure modes.
- Therefore, we connect the electrically loaded footing by a beam to the inner structure to balance or to reduce the stress concentration at the edge of the footing.
- There is an upward movement of the beam at the support due to the rotation induced by the load eccentric. It is like a cantilever.
- Therefore, these types of shallow foundations are called cantilever footings. In addition, these types of foundations fall under the spread footing.
Cantilever Footing Design
The cantilever footing design is the same as the strap footing design.
In addition to the bending stresses induced due to the vertical loads in the ultimate limit state, we have to consider the bending and shear forced-induced due to the load eccentric city.
The procedure to be followed during the design is discussed in the latter part of the article Strap footing. You may refer to that for more information and for work examples, you may refer to a different article.
Important aspects of Cantilever Footing
- Why need: Do we always need to connect the electrically loaded footing with a strap beam to an internal column. The answer is NO. Footings can construct with eccentricity. Footing can be designed for that. However, there are certain procedures to be followed by the designer.
- Avoid Load Eccentricity by New Column at Ground Floor: There are some modifications that can be made to avoid the eccentricity of the footing. One option is to shift the column starting to form the foundation towards the center of the footing and construct a floating column on the ground beam at the edge of the boundary.
- Cantilever the Beam: We can construct the column at the center of the footing and cantilever the beam at each floor level toward the boundary to extend the building.
- Construction: Construction of the cantilever footing foundation shall be done with much where there are weak soil layers. Ground improvement shall be done as recommended in the soil investigation report. Alos attention shall be made to the soil types and having expansive soils will make many issues in the design and construction.
Related Articles of Foundation Types
- Strap Footing
- Combined Footing
- Spread Footing
- Shallow Foundations
- Pier Foundation
- Footing Foundations
- Deep Foundations
- Foundation Failure
- Underpinning
- Eccentrically Loaded Foundations
- Shallow Foundation Failure
- Pile Raft Foundations
- Mat Foundation
- Pile Foundation
- Driven Pile Foundations
- Pile foundations
- Uplift Pressure on Foundations
- How to Determine Foundation Type
- Excavation for Foundation
- Foundation Waterproofing
- Settlement of Shallow Foundations
- Slab Foundations
