A strip foundation is a type of shallow foundation used in building construction. It is a continuous strip of concrete that is typically wider than the wall it supports and is used to distribute the weight of the building over a larger area of soil.
These foundations are commonly used for load-bearing walls, and they can be either reinforced or non-reinforced.
Types of strip foundation
- Traditional Strip Foundations
- Wide Strip Foundations
- Deep Strip Foundations
- Trench Fill Foundations
- Raft Foundations (a type of strip foundation)
1. Traditional
These are the most common type of foundations, consisting of a concrete strip that follows the perimeter of the external and internal load-bearing walls of a building.
2. Wide
These are similar to traditional foundations, but with a wider base that is used to spread the load over a larger area of soil.
3. Deep
These are used when the soil has a low bearing capacity or when the building load is heavy. The foundation is deeper and wider than traditional foundations to provide greater stability and support.
4. Trench Fill Foundations
These are similar to traditional foundations, but instead of excavating a trench, the foundation is created by pouring concrete directly into a trench or over a layer of hardcore.
5. Raft Foundations
These are a type of foundation that covers the entire footprint of a building.
The foundation slab is typically thicker than a traditional strip foundation and is used when the soil has a low bearing capacity or when the building load is heavy.
Raft foundations can also be used to provide a level base for a building on uneven ground.
Purpose of strip foundation
The purpose of a strip foundation is to transfer the weight of a building or structure to the soil below it.
These are used to support load-bearing walls and other structural elements of a building, such as columns or piers.
The foundation is designed to spread the weight of the building over a larger area of soil, reducing the pressure on any one point and ensuring that the building remains stable and secure.
These foundations are typically used in buildings with a relatively low number of stories, where the load-bearing walls are not too heavy. They are a cost-effective way of providing a stable base for a building and can be designed to suit a variety of soil types and ground conditions.
These foundations are also relatively easy to construct and can be installed quickly, allowing the building construction process to proceed more efficiently.
Thickness of strip foundation
As a general rule of thumb, the minimum thickness of a strip foundation should be 150mm (6 inches) for a single-story building with light loads.
However, for heavier loads or multi-story buildings, the thickness should be increased to provide adequate support.
What IS 1080 (1985) says about strip foundation
According to the Indian Standard IS 1080 (1985), the minimum width of a wall foundation must not be less than the sum of the width of the supported wall and 30 cm. This can be expressed mathematically as:
B = W + 30 cm
Here, B represents the width of the foundation at its base in centimeters, while W represents the width of the wall that is being supported.
For example,
if the width of the supported wall is 100 cm, then the minimum width of the foundation would be:
B = 100 cm + 30 cm = 130 cm
Therefore, the foundation must have a minimum width of 130 cm at its base to provide adequate support to the wall.
Advantages of strip foundation
1. Cost-effective
These foundations are cost-effective foundation options because they are relatively simple to construct and do not require extensive excavation.
2. Suitable for a variety of soil types
These foundations can be designed to suit a variety of soil types and ground conditions, making them a versatile option for building construction.
3. Relatively easy to construct
These foundations are relatively easy to construct and can be installed quickly, which can help to reduce the overall construction time and costs.
4. Can be designed to support heavy loads
These foundations can be reinforced to support heavy loads, making them suitable for a wide range of building types and designs.
5. Minimal disturbance to the site
These foundations require minimal excavation, which means that there is less disturbance to the site during construction.
6. Can be used on sloping sites
Stepped or sloping foundations can be used on sloping sites, which can reduce the need for expensive site leveling.
7. Can be used with other types of foundations
These foundations can be used in conjunction with other types of foundations, such as pile foundations or raft foundations, to provide additional support.
8. Can provide a stable base for the building
These foundations are designed to spread the weight of the building over a larger area of soil, which can provide a stable base for the building and help prevent settlement or movement.
9. Durable and long-lasting
These foundations are made of concrete, which is a durable and long-lasting material that can withstand a wide range of weather conditions and other environmental factors.
Disadvantages of strip foundation
1. Limited load-bearing capacity
These foundations are designed to support a limited amount of weight, which means they may not be suitable for larger or heavier structures. In such cases, more extensive and robust foundation systems like pile foundations or raft foundations may be required.
2. Susceptible to differential settlement
These foundations can cause differential settlement in the structure they support. Differential settlement occurs when different parts of the foundation settle at different rates, leading to uneven and potentially harmful stresses on the building.
This can lead to cracks, distortion, or structural failure in the building.
3. Inadequate for poor soil conditions
These foundations are not suitable for poor soil conditions, such as clay soils or soft soils that are prone to subsidence or liquefaction.
In such cases, alternative foundation solutions such as piling or ground improvement techniques may be necessary.
4. Unsuitable for uneven ground
These foundations require level ground conditions to be effective.
They may not be practical or suitable for sites with uneven or sloping ground, as they may need substantial excavation work and additional materials to achieve the required level of support.
