Raft foundations are meant to provide a rigid plate to transfer loads to a generally poor soil by distributing them over the entire area. They also provide a rigid base so that there is minimal differential movement between the building elements. They are modelled so that the slab and beam act compositely and often encapsulate portions of the poor soil with the beam grillage is confined and acts with the raft to reduce actual weight of the raft to reduce bearing pressures on the poor soil.
