Good foundation design is one of the most important aspects of a civil engineering project. Strip footing is a type of shallow foundation that is common for both residential and commercial applications. This article provides an overview of the design of strip footing principles, including material selection, footing shape, and analysis of loading. Professional civil engineers will find this information useful for designing cost-effective and structurally sound footings for their projects.
What is strip footing?
Strip footing is a type of foundation that can be used for buildings and structures that require more support than a simple slab foundation. Strip footings are typically installed in sloped areas to support the building from underneath. They can also be installed in uneven or irregular areas where it’s difficult to place other types of foundations. Strip footings are also known as raft footings, strip foundations, or strip foundations.
When designing a strip footing, the first consideration is the material that will be used. Concrete is the most common material for strip footing, due to its high strength and durability. However, other materials such as asphalt or stone can also be used in certain applications. The choice of material will be based on the specific requirements of the project.
There are two main types of strip footings.
- Strip footings with uniformly distributed load. It these types of footings, when there are not change in the loading and soil conditions, there won’t be considerable bending moment in shear forces in the longitudinal direction. However, there will be bending and shear force in the transvers direction which we must do the design.
- Footing will column load where the loads are applied as point loads.
Basic Steps of Strip Footing Design
- Select the suitable shape of the strip footing. This may be selected based on the type of loads.
- Finalized the load applied on the footing.
- Get the allowable bearing capacity of the footing from the soil investigation report.
- Calculate the area of the strip footing based on the service loads applied on it.
- Calculate the geometric center and the load center.
- Balance the footing press adjusting the length of the footing.
- Calculate the bending and shear forces.
- Calculate the reinforcement required for the footing.
Foundation design is a critical aspect of civil engineering. Strip footing is a common type of foundation that is used in both residential and commercial applications. This article has provided an overview of the design principles for strip footings. Professional civil engineers will find this information useful for designing cost-effective and structurally sound footings for their projects.
How to calculate the area of footing Dimensions
Let’s consider there are three columns, and each service axial load is as N1,N2 and N3
Allowable bearing capacity of soil as σall.
Area of footing, A = [ N1 + N2 + N3 ] / σall
Selecting the dimension of the footing is a trial-and-error process as we do not know any of the dimensions though we have the area of the footing.
Firstly, we assume the width of the footing and calculate the length of the footing. With that, we can reach the correct dimensions. In addition, it is required to consider the distance to the edge of the footing from the edge column. This distance shall be adjusted in a manner that there won’t be any eccentricity when we design the footing in the rigid method (manual calculation). The load center distance to the edge of the footing shall be similar. Then the pressure under the footing can be considered uniform.
The beam on flexible foundation theory can be applied to the strip footing design. This would be taken into account when the analysis is done using computer modes as manual calculations are more tedious in this method.
