Strip Foundation Vs Strip Footing Foundation

Every time, the size of the planned building structure depends on the soil conditions and might warrant the use of foundations that provide more stability for that condition than others. Several factors exist, such as waterlogging, rocky soil, erosion of construction materials that are strong enough to decide the strength of the structure or building foundations. Also, if wrong foundation building methods are chosen, it would require high labour and resource costs.

Footing Vs Foundation

Foundations are the best support providers for structures, transferring their load to the layers of rocks and soil with suitable settlement characteristics and excellent bearing capacity. From a broad point of view, one can categorize the foundations as either deep foundations or shallow foundations. When the loads imposed by a structure are low relative to the bearing capability of surface soils, then typically, shallow foundations are used.

What is Footing In Construction?

Footing is a part of the building structure for the safe distribution of the foundation. It is present at the bottom part of a foundation that supports the foundation and strengthens the base of a system.

In the cases when the rubble foundation is not readily available, your engineer may suggest the use of a strip foundation or strip footing foundation.

What is Strip Foundation or Strip Footing Foundation?

Strip foundation (or strip footing foundation) is a form of the shallow foundation built for providing a continuous and level (or stepped sometimes) supporting strip to a linear structure, like a wall or rows of columns built above them centrally. The everyday use of strip footing foundation is for the barriers that are intended to bear loads; and when the bearing capacity of the soil is good. However, it is preferred to use for low-rise to medium-rise buildings for residential purposes. Here runs a strip of concrete below the entire wall length that eventually distributes the load imposed on the walls to the ground. This provides better stability to the building.

But for this foundation building method, the width of the footing is required to be at least twice the width of the wall. The exact width of the footing and the load-bearing wall depends on the condition of the soil. Very broadly, the position and size of the strip are directly linked to the overall wall width. In general, the depth of a traditional strip foundation is greater than or equal to the wall’s overall width, and the foundation’s width is generally three times that of the supporting wall. However, the major design features of a strip foundation are dependent on the fact that the load transmission takes place at an angle of 45 degrees from the wall base to the soil. An experienced structural engineer might be able to guide you for this based on the soil test reports determined from your plot where the building is to be constructed.

There are also cases where a strip foundation is built to support a row of closely spaced columns. In such cases, a strip footing foundation or strip foundation is more economical than the spread footings that overlap each other. If the soil has a low bearing capacity, you may need to go with a wider strip foundation. However, plain concrete might not suffice in such cases. It is required to use concrete that is reinforced in such cases. Strip foundation can be built for most subsoils. However, it is best suitable for soil with relatively good load-bearing capacity.

Step by step procedure of Strip Footing

  • Find the positions of the walls that are supposed to bear loads.
  • Form a trench by excavating the site at these positions. Take care that the channel should be present below the centre of the wall above.
  • Pour lean concrete into the trench.
  • Install the main bottom bars after erecting the formwork.
  • Install the column starter bars.
  • Tie the column starter bars using binders.
  • Install the upper main bars.
  • Install the upper distribution bars.
  • Now fill the formwork with concrete.
  • You can remove the formwork once the concrete is set.
  • You can also use the excavated material for backfilling.

Final words

  • A strip footing foundation is not appropriate when the building has several columns with high localized loads. In such cases, pad foundation or isolated footing could be used.
  • When the soil’s load-bearing capacity is not sufficient to support the weight of the building or structure, pile foundations could be chosen.
  • It is advisable to go with deep foundations for buildings taller than 3 or 4 stories.

In short, these are the places where strip foundations should not be used.