When you combine footings, you reduce the cost and increase the stability of a building. Basically, when two or more footings are combined into one footing that is larger than any of the individual footings, it is called a combined footing. This technique can be used to provide structural support for buildings with difficult terrain on which to build. The combined footing distributes the weight of the building more evenly, which is especially important on soft or unstable ground. It can also help to prevent settlement and damage to a structure.
In addition, a combined footing can save you money because it requires less concrete than if each individual footing were built separately. And since it is larger, it will also require fewer footings, which means less excavation and labor. A combined footing also has the added benefit of being easier to pour than individual footings, since it is one large pour instead of several small ones.
If you are planning to build a structure on difficult terrain, or if you want to ensure that your building is as stable as possible, a combined footing might be the best choice for your project.
Advantages and Disadvantages of combined footings
Combined footing is a type of foundation/footing where the individual footings act as one. This should be used only if the soil conditions are very favorable e.g. sand, dry clay etc., It can also be applied to other types of soils provided that certain requirements are met.
The combined footing provides stability through increased bending resistance. In addition, the stability of the combined footing is not affected by minor movements of two adjacent footings due to settlement, rotation or temperature changes. These factors are very important in controlling building movement which can be a constant problem with a building of more than five storeys.
The reason for using a combined footing is because the soil behaves as a continuous mass and not as a number of individual soil elements. This results in the reduction of stress concentration at the footing edges.
The combined footing is also economical to construct, especially if the site has difficult access.
There are several other advantages of using a combined footing system for a building or structure. One of the main benefits is that it can help to distribute the weight of the structure more evenly, which can lead to increased stability and reduced settlement. Additionally, a combined footing can often be more economical than using individual footings for each column or pier, particularly if the soil conditions are favourable.
Another advantage of a combined footing is that it can help to reduce the potential for differential settlement. When different parts of a structure are supported by different footings, there is a greater risk of one part settling more than another, which can cause damage to the structure. A combined footing helps to minimise this risk by providing a more even distribution of weight.
Finally, a combined footing can also be easier and faster to construct than individual footings. This can be particularly useful in situations where time is of the essence, such as in emergency repairs. Overall, a combined footing can provide many benefits for a structure, making it a popular choice for many engineers and builders.
The main disadvantage of a combined footing is that it is difficult to construct in soils which are not homogeneous or which are compressible. Failure to follow the design procedure can result in differential settlement which can cause major problems later on.
Design of a combined footing
A footing is a foundation that supports the weight of anything constructed on top. The design process for a combined footing begins with understanding what will be placed on it, and how much weight it will have to bear. This article discusses the design considerations for a single-family residence, where only one footer is needed because the building does not exceed eight feet in height or span more than sixteen square meters.
The perimeter of the footing must be large enough to provide adequate stability; the minimum size is determined by applying a safety factor (SF) and multiplying it times something called “the critical area”, which depends on soil type and quality. The SF should take into account things like the weight of equipment, wind loads, earthquake forces, and more.
The critical area is the smallest rectangle that can encompass the entire load-bearing surface of the footing. The dimensions of this rectangle are then used to calculate the size of the footing by multiplying it by a standard dimension (e.g., 0.30 meters for residential footings).
Once the perimeter has been determined, excavation can begin
Once the perimeter is determined, a footing depth must be calculated to ensure adequate bearing capacity. The maximum allowable building settlement, as it applies here, should not exceed 0.25 inches per foot of vertical height under the load-bearing portion of the structure. In other words, if your house were one story tall and its design weight was 20,000 pounds, then the maximum allowable settlement would be 0.25 inches / 12 = 0.20 inch per foot of structure height (0.08 inch for a one-story house).
Types of combined footing
Different types of combined footings are as follows. A rectangular footing is the most common type and it will be used for a span that is not greater than 4 m or 13 ft. It can also be used in cases where there are no loads on the bearing surface except gravity loads. The trapezoidal footing can also be called an ‘open’ footing, because it does not have any width at the top surface. This means that this type of footing cannot resist any lateral load like shear or overturning moment unless supported by other structural elements such as walls, columns, beams etcetera. Lastly, we have tee shaped footings which act to transfer both axial and lateral forces from one structure to another when they are interconnected. This type of footing is used to resist overturning and lateral loads.
Each type of combined footing has its own advantages and disadvantages, so it is important to select the right one for the specific project requirements. Always consult with a professional engineer before starting any construction project!
Rectangular footings are by far the most common type of footing. They are simple to construct and can be used in cases where there are no loads on the bearing surface except gravity loads.
Trapezoidal footings, also known as ‘open’ footings, have a width that is less than their depth. This means that they cannot resist any lateral load like shear or overturning moment unless supported by other structural elements.
Lastly, tee shaped footings are used to transfer both axial and lateral forces from one structure to another when they are interconnected. This type of footing is used to resist overturning and lateral loads. Like the last two types mentioned above, it also has its own distinct advantages and disadvantages that need to be taken into account when making a decision.
So, which type of combined footing is right for your project? Always consult with a professional engineer before starting any construction project! They will be able to help you select the best option based on your specific needs. Thanks for reading.