Isolated footings are a type of structural element that serves to distribute and transmit loads of single columns to the soil without exceeding its bearing capacity. They also help to prevent excessive settlement and provide adequate safety against sliding and overturning. There are various types of isolated footings available such as spread footing, stepped footing, sloped footing, etc., and each type is chosen based on the soil condition and configuration of imposed loads. Isolated footings are typically square, rectangular, or circular in shape and are used when columns are spaced at relatively long distances.
Isolated footings are an economical type of footing that is used in the case of light column loads, when columns are not closely spaced, and in the case of good homogeneous soil. They are designed to prevent overloading of the soil and ensure that the weight of the structure is evenly distributed. The selection of the appropriate type of isolated footing depends on the type of soil and the load requirements. Spread footings, stepped footings, and sloped footings are commonly used types of isolated footings. Each type is designed to distribute the load evenly and prevent excessive settlement. Isolated footings are an essential element in the construction of many types of structures, and their proper design and construction are crucial to the safety and longevity of the structure.
Types of Isolated Footings
1. Flat, Pad, Plain, or Reinforced Isolated Footing
A type of footing that is commonly used in construction is the flat isolated footing. This type of footing is typically constructed independently under each column and can come in various shapes such as square, rectangular, or circular. The thickness of a flat isolated footing is uniform throughout. Its purpose is to reduce the bending moments and shearing forces at their critical sections.
Flat isolated footings can be constructed from plain concrete or reinforced concrete. Reinforced concrete is often used to increase the ultimate load carrying capacity of the footing. The use of reinforced concrete strengthens the footing and makes it more resistant to bending and shearing forces, resulting in a more durable and reliable foundation.
Overall, the flat isolated footing is an important component in construction that helps to distribute the weight of a structure evenly and provide stability to the building. Its uniform thickness and construction under each column independently make it a versatile and reliable option for various building designs.
2. Sloped Isolated Footing
Sloped or trapezoidal footings are constructed with a particular emphasis on maintaining a top slope of 45 degrees from all sides. This design approach is critical to ensure that the footing is stable and can support the load placed on it. Moreover, sloped footings require less concrete and reinforcement than plain isolated footings. By reducing the amount of materials used in construction, sloped footings can significantly decrease the utilization of concrete and reinforcement.
This reduction in material usage can have several benefits, including cost savings and increased sustainability. Sloped footings can be a more efficient and economical choice for certain construction projects, particularly those with lighter loads or those located in areas with stable soil conditions. Additionally, by using fewer materials, sloped footings can have a smaller environmental impact than traditional isolated footings. Overall, sloped footings are a valuable alternative for construction projects that prioritize efficiency and sustainability.
3. Stepped isolated Footing
In the past, isolated footings were commonly used in construction, particularly in residential buildings. However, their popularity has since declined. Stepped footings, which consist of three stacked concrete cross-sections resembling steps, are a type of isolated footing that is still used today.
Fig. 3: Stepped Isolated Footing