Spread footing is also called a spread foundation or spread footing foundation. What is a spread footing? It is a type of foundation designed and constructed to support superstructure elements such as steel or concrete columns, walls, etc. It is the most common type of construction done to rest the structure on the ground.
1. Introduction The size and weight of a building as well as the nature of the soil structure it is built on play a critical role in foundation design. Soil pressure distribution must be addressed to ensure a sound structure. Spread footing is a crucial structural component that provides strength for a building’s foundation.2. 3. Importance of Spread Footings

A spread footing foundation has a wider bottom portion compared to a load-bearing foundation; the wider bottom “spreads” the weight of the structure over a larger area for greater stability. While traditional spot footings only have a single point of contact with the foundation, spread footings extend support continuously across the entire building layout. Spread footings are used to support a foundation or set of piers below a building. To add additional support, spread footings are constructed with concrete and reinforced with steel. Since spread footing transfers the weight of the building over a large area, spread footings have little risk of failure compared to spot footers. Spread footing extends the life of a building by minimizing structural damage. Footings must be designed to carry the column loads and transmit them to the soil safely. Spread footings may be circular, square, or rectangular. Spread footings are common in residential construction.

4. Mode of Distribution of Soil Pressure in a Spread Footing Column loads act at the center of the footing, creating a uniform surface for the soil underneath the footing area. The distribution of pressure depends on the composition of the soil and on the degree of flexibility of the footing.5.

• Types of Spread Footings: (i) Isolated Footing When columns are spaced far apart, isolated footings are used to support single columns.
• Ii) Combined Footing When two columns are close to each other and their individual footings overlap, a combined footing is required.
• A combined footing supports two columns so that the load is evenly distributed.

A combined footing may be rectangular or trapezoidal. (iii) Strap Footing (Cantilever) In strap footing, two isolated footings are connected with a structural strap (rigid beam) or lever. (iv) Mat Foundation (Raft) A mat foundation is a large slab that supports several columns and walls under the entire structure.

What is a spread footing base?

The spread footing is used to support the column and walls and also transmit and distribute the load coming on the structure to the soil below it. With loads applied in the upward direction, this footing behaves like an inverted cantilever, and this type of footing is quite rigid element & they are orthogonal in case of symmetric footing. A spread footing base is wider than a typical load-bearing wall foundation and spreads the weight from the building structure above more area and provides recommended stability. Where the bearing soil layer is within 10 feet from the ground surface, this type of footing is used for individual columns, walls, and bridge piers.

What is a spread Foundation?

What Is Spread Footing and How Does It Work? – Spread footings are utilised in the construction of the building to provide a stable foundation for the columns and walls, The load from the structure is delivered and transmitted to the ground via spread footing.

1. A shallow foundation is known as a spread foundation.
2. Spread foundations are often employed as a building’s foundation.
3. The spread foundation extends or spreads to the structure’s individual support curves.
4. Open excavation is commonly used to build spread foundations.
5. This sort of footing can come in a variety of shapes, including round, square, and rectangular.

To transfer the building’s high load, this form of footing is sometimes done utilising a step approach.

How many steps are there in a spread footing?

Isolated Footing – Isolated footing is also known as column footings is the most common type of shallow foundation constructed in the world. Further, due to the simplicity of the shallow foundations, design, and construction is simpler when compared to the other type of foundations. The design of this type of spread footing is that complicated. Only there are several steps to be followed.

Calculate the size of the footing based on the applied load and allowable bearing capacity.

A = F / σ where, A – area of the footing, F – Column load (serviceability limit state) and σ – allowable bearing capacity

Calculate the Pressure under the foundation in the ultimate Limit State

σ U = P / A were, σ U – Ulitmate pressure under the footing, P – ultimate axial load

Calculate the Bending moment at the face of the column and find the reinforcements.Check whether it is required to band the reinforcements.Check the verticle line shear at the face of the column. It should be less than the maximum allowable shear stress in the concrete.Check the punching shear capacity of the footing. The article Punching Shear could be referred for further information.

There are types of isolated spread footing foundation types such as

Uniform thickness footings: The thickness of the footing remains the same. Varied thickness footing: The thickness of the footing varied and it increases toward the column. This is a cost-effective method but attention shall be made to the thickness of the column as it is critical. There are possibilities of making construction errors in these types of footings. Stepped Footings: Instead of the slope, there are steps at the top of the footing. The number of steps may depend on the size of the footings. Generally, steps are constructed to cover the punching shear perimeter for enhancing the shear strength of the spread footing.

How is the load distributed on a spread footing?

Spread Footings Definition of Spread Footings in Construction The term spread footings, refers to the distribution of structural loads that bear down on a concrete footing. The spread footing is a structurally designed combination of reinforcing steel and concrete.

This design will allow the load placed on the footing to be distributed throughout the square footage of the entire spread footing. Therefore, if a one foot square column is bearing down on the center of a four by four spread footing, the actual weight distribution of the one foot square column is now spread over sixteen square feet.

This distribution of the load will reduce the overall load on the soils below the spread footing from the one foot column load to a sixteenth of this load, due to the added square footage of the spread footing. The lower the bearing capacity of the soil, the larger the spread footings must be designed to accommodate the load.