A strip footing is a long continuous strip of concrete used to distribute the weight of a load-bearing wall over a floor area. A constant concrete strip is placed under a load-bearing wall in strip foundations. The foundation can be made of either plain concrete or reinforced concrete. Strip footing is the most popular type of footing. Strip width is determined by permissible ground pressure and building load.
The strip should be long enough to rest on firm ground. If the soil is weak and the load is heavy, a more comprehensive foundation is required to distribute the weight over the surface of the earth. Soil properties also determine depth. For example, in clay soils, the footing should be deep enough not to be affected by volumetric changes due to the seasonal movement of trees. A fine sand, gravel, and silt depth are required to minimise frost heaving.
See also: What is screed concrete and where is it used?
What is strip footing?
Strip footings are commonly used as foundations for load-bearing walls if the ground is a suitable bearing. It is ideal for low to medium-rise residential buildings. A concrete strip runs the entire wall length, distributing the load from wall to floor. This increases the stability of the structure. For this reason, the width of the foundation should be at least twice the width of the wall.
In some cases, strip foundations support a series of closely spaced columns. In such cases, strip foundations are more economical than stacking continuous foundations.
If the soil has a low load-bearing capacity, it may be necessary to use a comprehensive strip foundation. In such cases, you may require more than plain concrete. In place of bare concrete, reinforced concrete should be used. The exact width of supporting walls and foundations depends on soil conditions. A structural engineer should be able to guide you based on soil test reports on your property.
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Construction of a strip footing
- Locate the load-bearing wall.
- Excavate the terrain at these locations to form trenches. The trench should be centred on the top wall.
- Fill the lean concrete.
- Set up the formwork and assemble the lower main bars. Following this, the column starting bar is installed.
- Ties are used to tie the starting poles of the columns.
- The next step is to install the top main bar.
- Then install the upper distributor rail.
- Pour the concrete into the formwork. Constructors can remove the framework after the concrete set.
- Constructors also use excavated material for backfilling.
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Strip footing: Types
Based on its properties, strip footing comes in two types.
Deep strip footing
The most common type of footing is the deep strip footing, which is most favourable when soil conditions are right—strips of reinforced concrete support the walls. The groove depth is arbitrary but should be at least 40 inches deep and 24 inches wide. Concrete should be at least 9 inches deep.
Broad strip footing
Broad strip footings are present in areas with poor bearing capacity soils. Poor-quality soil does not allow a regular strip footing. Overwidening or deepening a structure to avoid demolishing walls is not economically justified. Building the foundation using reinforced concrete can be a suitable solution. Reinforcing bars provide tensile strength to foundations so that the entire structure can withstand stress and compression.
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Strip footing: Benefits
Strip footing offers considerable advantages wherever civil engineers can use it judiciously.
- In terms of construction and materials, they are relatively cheap.
- Construction of strip footing is quick and straightforward, requiring only the most straightforward formwork construction and rebar installation.
- Both architectural professionals and artisans understand them well.
Slip footing: Limitations
- Strip foundations are suitable only for relatively small construction projects with relatively low load requirements.
- If the ground is weak or uneven, strip foundations can have severe consequences, lead to structural integrity problems and even collapse.
- Strip footing may also not be suitable on slopes or where retaining walls are required.
FAQs
How to know if strip footing is suitable for use?
When planning a building project, consider the width of the foundation strip as specified by the building code. The concrete solution must meet compatibility with soil chemicals.
What is the principal design feature used in strip footing?
The size and position of the strips are directly related to the overall width of the wall. An essential design feature of strip foundations is based on the fact that loads are transferred from the building base of the wall to the ground at an angle of 45 degrees.
Where is strip footing used?
Strip footings are commonly used for bearing walls. The ground is usually twice as vast as the supporting wall, sometimes even more expansive. The width and type of reinforcement depend on the load-bearing capacity of the subsoil.
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