Building Foundation Types for Construction Engineering
This article is about Building Foundation Types. Living in construction world, Civil Engineers must know the Building Foundation Types. Understanding this Building Foundation Types will let the engineers have many option to design the correct foundation type for the building they are constructing. For your information, In construction, Foundation can be called as Footing also.
What is Foundation or Footing?
Foundation substructures are structural members used to support walls and columns to transmit and distribute their loads to the ground. Or let us say, foundation or footing is the lowest part of the structure that distributes the load on a larger area to avoid any shear or axial failures of the structure.
What to consider when we are designing Foundation or Footing ?
When we are deciding to choose one of Building Foundation Types, we have to consider several things. For proper transmission of the load the substructures must be designed :
- To prevent excessive settlement
- To prevent rotation
- To minimize differential settlement.
- The load bearing capacity of the soil is not exceeded.
- Adequate safety against sliding and overturning is assured.
Cumulative floor loads of a building, a bridge, or a retaining wall are supported by the foundation substructure in direct contact with soil. The soil underneath the substructure becomes compressed and deformed during its interaction with the substructure. This deformation is the settlement that may be permanent due to dead loads or may be elastic due to transition live loads. The amount of settlement depends on Type of soil, The load intensity, The ground water conditions, The depth of the foundation below ground level.
After you consider the things mentioned above, you have to choose one of these Building Foundation Types. Please check the following list :
Isolated Spread Footings
Mostly in a frame structure (having beams and columns) the foundations for a column is isolated or spread footing. These footings are used to carry loads of individual columns. Isolated spread footing may be in any shape like rectangular, square or circular depending upon design requirement.
The footing may be of uniform thickness, stepped, or even have sloped top and reinforced in both directions.
Wall Footings or Strip Footing
Mostly when the walls are load bearing, as in the case of flat plate slab when the slab is directly resting on the walls than the load of such walls is transmitted using wall footing or strip footing. It is in limited width and continuous slab strip along the length of the wall.
In case of closely spaced columns it is more economical to combine their footings in such a way that footings of two or more columns are combined in a rectangular or trapezoidal plan. The combined footing becomes necessary in situations where a wall column has to be placed on a property line that may be common in urban area. Under such conditions, an isolated footing may not be suitable since it would have to be eccentrically loaded. It is more economical to combine the exterior column footings with an interior column footing.
Strap Footing or Cantilever Footing
For eccentric column load at the exterior column (possibly located along the property line) the effect of the bending moment produced is transferred to the interior column footing using a strap beam.
Mat, Raft or Continuous Footing
In case when the soil conditions are poor and a pile foundation is not economical than the load of the columns is transferred to a mesh or a mat supporting all of the columns.
This type of foundation becomes essential when the supporting soil consists of poor layers of material to an extended depth such that an individual or mat foundation is not feasible.
The writing above is inspired by Saad Iqbal, an Engineer currently working in NESPAK. I hope he get benefit from what he wrote. And I hope you can get benefits from this Building Foundation Types article too. If you want some updates, please subscribe. Please share if you think this might be useful for your community. Thanks.