Residential concrete slabs are the most common footing and flooring systems in Australian residential construction.
What is a Raft Slab?
Slabs are structures that interface between floors of a building and can support subfloors or function as a ceiling. Generally, they rest on beams, which in turn rest on pillars and adequately distribute the building load.
Its structural design is of a plate in which two dimensions are much larger than the third, which is the thickness, with loads transverse to it and subjected to bending. The design criteria are the breaking strength and the thickness itself. Thin slabs may be safe to break, but cause user insecurity due to large arrows or excessive vibration.
A raft slab is reinforced concrete slab on ground that is strengthened with integral concrete beams in both directions. Raft foundations can be fast and inexpensive to construct, as they tend not to require deep excavations compared to strip or pad foundations and they may use less material as they combine the foundation with the ground slab.
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.
- Ground conditions are poor and strip or pad foundations would require significant excavation, for e.g on soft clay, alluvial deposits, compressible fill and so on.
- Settlement, or differential settlement is likely.