Isolated Footing: Types, Advantages & Disadvantages
Isolated Footing is specially constructed for single-column. The structural load of the construction structures has been distributed evenly across the soil by isolated footing which helps to reduce the risks of sinking or settling. Various materials including steel or concrete are used for constructing isolated footing in building construction. This is the most simple and cost-effective and also the most widely used footing in building construction. Isolated footing is used in case of the column load is light and the soil of the construction unit is homogenous. Isolated footing can be reinforced or non-reinforced and supports the individual columns that are arranged at a long distance.
Advantages of using Isolated Footing
Several advantages are provided by isolated footing in building construction. These advantages include:
The distribution of the load
The individual load of the construction structure has been supported by isolated footing. The loads are distributed evenly by isolated footing which helps to prevent the transfer of excessive weight to the neighbouring areas or columns.
Exhibit versatility in construction project
Isolated footing can be applied in board structures. The adaptability of this type of footing is suitable for various types of architectural designs.
Simple designs
The simple designs and construction process of the isolated footings help to streamline the implementation of these footings on the construction sites and also increase the cost-effectiveness.
Reducing the risk of settlement
Isolated footing helps to ensure the uniform settling of the building structure thus reducing the chances of uneven foundation.
Cost-effective process
The straightforward design of isolated footing helps to save the overall cost of the construction project.
Simplifying the inspection and maintenance process
The nature of these footings helps to simplify the inspection and maintenance procedure.
Suit different soil conditions
The isolated footings suit different types of soil conditions. The adaptability of this type of footing has been increased by customising the size and depth of these footings on the basis of the load-bearing capacity and characteristics of the soil.
Disadvantages of using Isolated Footing
➢ In the case of tall and high-rise building structures, the small size of isolated footing is not appropriate for supporting against the tilting.
➢ More time and effort are required to install multiple isolated footings on the construction site.
➢ It has limitations in supporting maximum loads of the larger structures.
➢ The effectiveness of the isolated footings depends on the site-specific conditions. In this regard, unforeseen changes in site conditions are challenging for the effectiveness of the isolated footings.
Different types of isolated footings
Three types of isolated footing are available which include:
Isolated spread footing
This is also known as isolated pad footing or isolated flat footing. This type of footing is available in rectangular, square and circular shapes and can be constructed independently under each of the columns. The bending moments and the shearing forces have been reduced by isolated spread footing.
Isolated sloped footing
Isolated sloped footing is also known as isolated trapezoidal footing which is designed for maintaining 45 degree angle from all sides. In this case, the requirement for steel and concrete is lesser. So, it is a cost-effective option in a construction unit.
Isolated stepped footing
In residential projects, this type of footing is used. In this isolated stepped footing, 3 concrete cross-sections are stacked upon each other which helps to to give the step’s shape.
Availability of isolated footings at different shapes
Three common shapes of isolated footings are: Square, Circular and Rectangular
How isolated footing available at different shape
There are two ways in which isolated footings take shapes which include:
Excavation and Preparation
The construction procedure has begun with the excavation of soil into the specific depths which helps to create the pit for the isolated footing. The depth and size of the soil excavation depend upon the conditions of the soils as well as the load-bearing requirements.
Reinforcement and Placement of the Concrete
Reinforcement bars, or rebar are placed in the excavation area which helps to enhance the footing’s strength. After the reinforcement, the concrete is poured which helps to create a solid base.
Isolated footing designs
The objectives that should be considered for designing isolated footings are:
➢ Determine the dimensions of the footing such as the length footing, width of footing and thickness of the footing
➢ Calculating the development length
➢ Estimating the load-bearing stresses
➢ Estimating the reinforcement that is required in terms of area of steel
Steps followed in designing isolated footing
Several steps which are important while designing footing:
➢ Find out the area of footing
➢ The suitable thickness of the footing should be assumed
➢ The critical sections for footing should be identified for shear and flexure
➢ The shear forces and the bending moments at the critical sections should be found
➢ The adequacy of the assumed footing thickness should be checked
➢ The reinforcement detailed should be found
➢ The development length of the footing should be checked
➢ The load-bearing stress should be checked
To learn more, watch the following video tutorial.
Video Source: AK Skills & Solutions
Requirement for designing isolated footing
The design requirements for isolated footing are:
➢ The load of the column
➢ The size of the column
➢ The grade of the steel, for example, Fe415, Fe500, and others.
➢ he grade of the concrete, for example, M20, M30, and others
➢ Soil’s safe bearing capacity
