# What is a raft foundation design?

## What is a raft foundation design?

A raft slab is a reinforced concrete slab on ground that is strengthened with integral concrete beams in both directions. Usually, a raft slab is used as the foundation for new houses and extensions. Raft slabs in Australia are designed to comply with Australian standard AS2870.

## How do you calculate raft foundation design?

A = total area of the raft. = eccentricities about the principal axis passing through the centroid of the section. = moment of inertia about the principal axis through the centroid of the section. = eccentricities in x and y direction of the load from the centroid.

How is a raft foundation constructed?

Raft Foundations are built is this following steps:

1. The soil removed down to correct depth.
2. The foundation bed is then compacted by ramming.
3. Lay reinforcement on spacers over the foundation bed.
4. Pour the concrete over the reinforcement.

### What is the minimum depth of raft foundation?

300mm
The minimum thickness of raft foundation is 300mm.

### Where are raft foundations used?

Raft foundation is generally used to support structures like residential or commercial buildings where soil condition is poor, storage tanks, silos, foundations for heavy industrial equipment etc.

What are the advantages of raft foundation?

• Mat foundation can be provided where the shallow foundation is necessary but soil condition is poor.
• It resists differential settlement. •
• Mat foundation itself can be considered as a floor slab. So it reduces the cost of constructing floor slab.
• Distribute loads over a larger area.

#### What are the disadvantages of raft foundation?

• Raft foundation is prone to edge erosion.
• Raft foundation requires more amount of reinforcement in some cases, and it will ultimately cost more.
• Skilled labours are required as compared to other foundation.

#### How do you find the minimum depth of a foundation?

Minimum depth of foundation as per IS 1080-1982 is 500mm from Ground Level. 2. As per Rankine’s theory Minimum depth of foundation =p/w (1-sin Φ /1+sin Φ) 2 where p=gross bearing capacity w =density of soil Φ =angle of response of soil 3. But in practice, the foundation depth is kept at 0.90m or even more.

What are the three types of raft foundation?

There are five main types of raft foundation:

• Solid slab rafts,
• Slab beam rafts,
• Cellular rafts,
• Piled raft foundations; and,
• Balancing (or floating) rafts.

## When would you use raft foundation?

They spread the load imposed by a number of columns or walls over the area of foundation, and can be considered to ‘float’ on the ground as a raft floats on water. They are suitable where: Floor areas are small and structural loadings are low, such as in one or two-storey domestic construction. A basement is required.

## What is raft foundation construction?

Mat foundations also are known as raft foundations, is a thick concrete slab placed on the ground as the foundation of the structure. Mat foundations are constructed on various occasions such as building construction, bridge construction, tower construction, etc.

Where would raft foundation be used?

Raft foundation is generally used to support structures like residential or commercial buildings where soil condition is poor, storage tanks, silos, foundations for heavy industrial equipment etc. To get a better idea about when to use raft foundation, it is important to understand how raft foundation works.

### What are the analysis methods for raft foundation?

Raft foundations can be analysed using the rigid approach or flexible approach. The conventional rigid combined footing approach is a method of analysing raft foundation using simple statics without any consideration of the elastic properties of the raft and the soil and their interaction.

### What is the meaning of raft foundation?

A raft foundation, also called a mat foundation, is essentially a continuous slab resting on the soil that extends over the entire footprint of the building, thereby supporting the building and transferring its weight to the ground. A raft foundation is often used when the soil is weak, as it distributes the weight of the building over the entire area of the building, and not over smaller zones (like individual footings) or at individual points (like pile foundations ).