The spread footing is utilized to transport and distribute the load arriving to the formation to the soil underneath it as well as to support the column and walls of the building.
When there is symmetric footing, this form of footing is frequently a stiff element, and they are orthogonal by default. This foundation really acts like an inverted cantilever when weights are applied upward.
This kind of foundation can take the shape of a slab that is homogeneous in thickness and can be round, square, or rectangular; it may also be stepped to assign the weight over a wide area.
In comparison to the base of a load-bearing foundation, spread footings are a little bit broader. This is also known as a spread foundation with steps.
This type of footing consists of the construction of an RCC member-based base foundation. This deeper bottom spreads the weight across a larger area, which strengthens the structure.
Since they are designed differently from conventional spot footers, the spread footings are made of concrete and steel and are less prone to fail.
The article below covers everything you need to know about spread footing.
What are the Different Types of Spread Footing Foundation?
The building industry frequently use the spread foundations. For individual support, the structure’s base enlarges or spreads. Read below to know the varied types of spread footing foundation.
1. Foundation Raft.
In essence, a raft foundation, also known as a mat foundation, is a continuous slab sitting on the ground that covers the whole footprint of the structure, supporting it and dispersing its weight to the ground.
Raft foundation is basically a combined footing that covers the entire region immediately beneath a structure and supports all the walls and columns.
An R.C.C. slab of the appropriate thickness is supplied in this foundation, either with or without a beam.
2. Footing for Grillage
A foundation for grilling is made out of one, two, or more levels of beams (usually made of steel) layered on top of a concrete layer to distribute the weight over a vast area. Usually, heavy-structured pillars and column scaffolds employ this kind of base.
When using low-bearing-power soils, a grillage footing is used to transfer heavy loads from the steel column.
3. Inverted Arch Footing
When compared to a typical arch bridge, an inverted arch, also known as an invert, is a civil engineering construction. The arches merely disperse the downward loads of the viaduct piers onto a larger ground surface, much like an inverted arch bridge, in the simplest case.
This type of foundation is used in locations where the soil’s bearing capacity is extremely low, the load of the building is concentrated on the walls, and extensive excavations aren’t feasible.
4. Continuous Footing
When more than two columns are supported, the footing is said to be continuous. The footing is comparable to a wall‘s strip footing. When the weights are heavy, a longitudinal beam that runs lengthwise is used to transmit the loads from the individual columns instead of straight to the foundation slab.
This kind of foundation reduces differential settling and is appropriate for earthquake-prone areas.
5. Strap Footing
A strap footing is a component of a building’s foundation. A concrete beam linking two or more column footings makes up this type of composite footing. This type of beam includes strap beams.
A strap footing is composed of two or more independent footings connected by a strap beam. Other names for it are pump handle foundation and cantilever footing.
6. Combined Footing
A strap footing is a component of a building’s foundation. A concrete beam linking two or more column footings makes up this type of composite footing. This type of beam includes strap beams.
A strap footing is composed of two or more independent footings connected by a strap beam. Other names for it are pump handle foundation and cantilever footing.
The term “mixed footing” or “combined footing” refers to when a single footing must handle two columns, or in rare circumstances more. We give a single foundation for two or three columns that are situated quite close to one another, and the footing is referred to as a combined footing.
This type of footing is created when two or more columns are present in a row. There are two different types of footing in this:
- Combined rectangular footing. Columns are same or uniform.
- Combined footing with a trapezoid form. There are space restrictions and no equivalent or identical columns.
7. Isolated footing
The single or individual footing known as an isolated footing is what distributes weight to the subsurface earth. When a single column is required, it is given. The portion of the substructure that rests inside the ground or has direct contact with it is known as the foundation.
For a single column, this style of footing is used. These three forms of isolated footing are further divided into:
- Stepped footing
- Sloped footing
- Simple spread footing
8. Wall Footing
A continuous strip of concrete known as a wall footing or strip footing is used to distribute the weight of a load-bearing wall over a soil area. It is an essential part of a thin foundation. Both reinforced concrete and ordinary concrete can be used to build wall footings that support direct vertical loads.
Most wall footings are either straightforward or steep. Wall footing can also be divided into two categories:
- Simple wall footing
- Stepped wall footing
Spread Footing Design
- To begin, we must ascertain the sizes and structural loads of various elements at the base of the structure.
- Next, we must gather information and establish the planned footing.
- Next, we decide where to place the footing element and its depth.
- The soil’s holding capability must also be determined.
- The strength of concrete is also measured, followed by the total and differential settlement.
- Next, we decide on the thickness, footing measurements, and steel grade.
- Following this procedure, we design the relationship between the foundation and superstructure.
- We verify the durability and elevation against sliding situations last.
What is Concrete Spread Footing?
The footing’s depth needs to be adequate to adequately withstand punching shear and direct shear caused by column stress. The reinforcement for the footing should also be constructed to withstand bending moments.
The dowels that are offered at the column-footing interface should be able to transmit column load. Spread footings are built using concrete and steel reinforcement for added stability.
Spread Footing vs. Mat Foundation
Spread Footing:
- A single column is supported by a spread footing, also known as an isolated footing or a pad footing.
- A spread footing is a consistently murky round, square, or rectangular slab.
- It is sometimes stepped to distribute the weight across an excessively large region.
- Residential structures frequently have spread footing foundations, which have a bottom component that is broader than the load-bearing foundation walls they support.
- For improved stability, this broader section “spreads” the structure’s weight across a larger area.
Mat or raft foundations:
- A mat or raft foundation may be a huge slab supporting a variety of columns and walls beneath the whole project or a sizeable piece of it.
- A mat is required if the columns and walls are so near that the individual footings would overlap.
- Mat foundations can aid in reducing the differential settlements when the soil is not homogeneous or when the weights on the individual columns vary widely.
- The entire building area is distributed with substantial wall and column loads thanks to mat-slab foundations.
- Basements or areas near the ground’s surface can have mat-slab foundations constructed below them.
What are the Benefits of Spread Footing?
The benefits of spread footing include,
- Spread footing is among the simplest forms of footing, making it simple to build.
- It comes in a wide range of forms, including rectangular, square, round, etc., and is employed according to need.
- Due to the soil’s capacity to disperse building loads over a vast region, the forming pressure on the supporting soil does not exceed the soil’s permissible bearing.
- Spread footing construction is inexpensive thanks to its cost-effectiveness.
- Laborers can complete the construction process; professionals are not necessary.
- Materials are readily available and nearby.
- Given how easily a structure can be built, there is virtually little chance that it will fail.
Shallow Spread Footings
It is referred to as a shallow or stepped foundation if the depth of the foundation is less than the breadth of the foundation.
Instead than using a subterranean layer or a variety of depths as in a deep foundation, a shallow foundation essentially distributes building weights to the soil extremely near to the surface.
When building a structure on soil that must have a maximum bearing capacity, this method may be utilised. This Foundation has a minimum depth of 800 mm and a maximum depth of 4 metres.
Spread Footing FAQs:
1. What are the disadvantages of spread footing?
1. Not suitable for all types of soil.
2. The entire lot must be filled at once, although it can be challenging to prepare that much concrete alone.
3. You will want assistance because pouring the concrete requires a lot of work.
