What is raft foundation and explain its purpose?

Raft foundation is a thick reinforced concrete slab which spreads over a large area of soil and provides support for several columns and load bearing walls. It is also called as mat foundation which are widely used foundation system. Raft foundation is a type of shallow foundation.

Why raft foundation is provided?

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). This reduces the stress on the soil.

What is raft foundation when is it preferred?

a) Raft foundations are preferred in areas with poor soil bearing capacity, uneven settlement, and the presence of mixed soil types. These foundations achieves the load-bearing capacity through the distribution of stresses to a larger area.

What is raft foundation in civil engineering?

Raft foundations are a type of foundation with high integrity in which four foundation piers are connected together using a large foundation slab to form a massive structure and the foundation piers are connected through beams.

How does a raft slab work?

Raft slabs consist of a thick steel reinforced slab that is integrated with steel reinforced beams, which are dug into the ground for added strength and support. It’s also more suited to sloping blocks as the edge beams are dug into the ground and working the slab into the soil and slope.

Where are raft footings 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 is the difference between pad foundation and raft foundation?

Pad foundation refers to the foundation which is intended for sustaining concentrated loads from a single point load such as structural columns. Moreover, raft foundation serves to avoid differential settlement which otherwise would occur if pad or strip foundation is adopted.

How do you calculate reinforcement in raft foundations?

Calculation of reinforcement on both axis In both axis, reinforcement is calculated based on the maximum moment at that strip in both direction. For a axis, normally the strip with maximum moment is taken and same amount of reinforcement is placed in all footing area in that direction.