What are Footing Types and Design Method?
Whether you are a construction manager, a contractor, or just building your own home, you will need to know what type of footing you need. There are several different types, including concrete, gravel, strapping, and rafting. Each footing type has different strength requirements, failure modes, and design criteria. Identifying what type of footing you need for your project will ensure that you get the best results.
Concrete
Several types of concrete footings are designed to resist soil pressure. Plain concrete footings and reinforced concrete footings are used to support walls and column foundations. Reinforced concrete footings are used in areas with very poor soil bearing capacity. Often, they are used to support cast-in-place concrete foundation walls.
Plain concrete footings are used in areas with normal soil bearing capacity. They have been designed according to the results of finite element analysis. These calculations are usually based on the design code. The footing’s size and thickness are determined according to the design bending moment at the face of the wall or column. A column footing may be made of stone masonry, brick, reinforced cement concrete, or steel. It is used to distribute load below the soil in a uniform manner.
Also read about, Why Are I Beams Using in Structural Steel Construction?
Gravel
Depending on the soil type, gravel footings are oftentimes the only way to go. These types of foundations are typically supported by a preservative-treated wood wall and floor system. Gravel footings are typically composed of pea gravel, crushed stone, or a combination of the two. The footing is constructed by vibrating and tamping the aggregate, resulting in a smooth surface. Depending on the soil type, the footing may be buried under a layer of cement. This method of construction is typically the most cost-effective and the best choice for your next home improvement project. Typical footing depths range from a minimum of 12 inches in the South to as much as six feet in the northern hemisphere. A gravel footing may be considered as part of your home improvement project. The footings main benefits include improved drainage and a more solid foundation.
Strap
Generally, a strap footing is a unique type of combined footing, usually a single beam connecting two individual footings. This structure is designed to minimize differential settlement between sections of a building. The strap is not meant to bear weight, but to transfer the eccentric moment between the two footings. In addition, it can tie two different notches together. It can be constructed with a number of different methods, but a ridged strap is the cheapest way to do it. A strap footing is often constructed in reinforced cement concrete. A strap footing is typically used to support two columns. A strap footing is also useful when the base of an exterior column needs to not protrude beyond a property line.
Raft
Several types of raft footings exist, with different design methods. These types of footings are useful when a structure is subject to uneven soil or if the soil’s geo technical capacity is insufficient for isolated footings. The main advantage of raft foundations is that they are cheaper and safer than isolated column footings. However, the design method for these foundations is complicated and requires sophisticated software. The conventional rigid combined footing approach for analyzing a raft foundation does not take into account the elastic properties of the raft. Instead, it analyzes the raft as a large beam member. The moment per unit width is determined by dividing the moment values by the section width. The Winkler method was designed to account for the elasticity of the footing. Specifically, it assumes that soil behaves as an infinite number of independent elastic springs. The centroid of the soil pressure coincides with the line of action of all the loads acting on the foundation.
Failure Modes
Generally, failure modes of footings in areas with slopes are divided into two main modes. These modes include bearing capacity failure and overall slope failure. Bearing capacity failure is a major issue when designing a footing for a slope. Basically, this is a failure where the footing will not withstand the load and will collapse. There are many factors that contribute to bearing capacity. For example, the foundation must have a high resistance against swelling pressure. It must have a good adhesion between the base and the soil. It also must have a good resistance against lateral forces. One way shear failure is characterized by the failure of a foundation in inclined cracks that extend across the full width of the footing. These cracks are usually located at a distance d from the face of the column. The distance d is measured from the halfway point between the face of the column and the edge of the base plate.
Footing is an essential part of any structure, as it is the key element transferring load safely from the structure to the ground. If you have faced any issues with footing replacement services then you need to hire footing contractor Boston. We are here at XStructural to help you. For more information you can contact us on (617) 304–1462 and email us on info@xstructural.com
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