What are the Thickness Requirements for Strip Footing?

05 March 2019

Strip footing, also known as spread footing or wall footing, is meant to establish a shallow foundation typically for load bearing walls of various sizes. Support slabs are placed into a trench as a strip of concrete and are reinforced with steel.

Various configurations are used to strengthen these strips, such as tee or inverted tee strip footing, depending on the need and the pre-determined width of the strip footing foundation, and the estimated bearing capacity of the subsoil underneath. A subsoil that has a greater bearing capacity will require lesser foundation width and depth.

The required thickness for strip footing is determined by a number of factors. These factors include such things as the type of soil at the location and the needed depth of the foundation. The other main factor that will determine the thickness of strip footing is the load conditions.

Thickness Requirements for Strip Footing Foundation for Carrying Light Loads

The minimum thickness for strip footing foundation should not be less than 150mm, but it can be equal to the projection of the face of the foundation to the trench wall. This will ensure that the strip footing foundation has enough rigidity to handle the bridge pockets in the subsoil, and to endure longitudinal force cause by any expansion or movements of the footing wall.

If the subsoil underneath the strip footing is clay, then the minimum thickness of the strip footing is absolutely necessary to withstand the swelling of clay, and the pressure it will impose on the foundation.

Thickness Requirements for Strip Footing Foundation for Carrying Heavy Loads

Determining the thickness requirements for strip footing foundation for carrying heavy loads is not a simple task, as it should be thick enough to withstand shear and bending movements under extreme weight that could cause the footing foundation to fail. It is possible to avoid bending failure, by employing thick layers of concrete applied in a stepped or slopped transition, to a determined thickness needed from the bottom of the width to the face of the wall.

However, that thickness needs to be determined by the onsite contractor installing the strip footing foundation, but typically the thickness is equal to twice the length of the projection on the strip. Because setting strip footing is a labour-intensive work, contractors prefer to hire mini diggers to get the job done, as these are affordable and efficient at digging trenches, and small enough to work in tight spaces.

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