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History of concrete slabs
1. A concrete slab is a common structural element of modern buildings. Slabs that are most often used to construct floors and ceilings are typically between 4 and 20 inches (100 and 500 millimeters) thick. While thinner slabs are used for exterior paving range from 2 inches (51 mm) to 6 inches (150 mm) thick. In many domestic and industrial buildings, a thick concrete slab, supported on foundations or directly on the subsoil, is used to construct the ground floor of a building. The slab is "ground-bearing" if it rests directly on the foundation, otherwise the slab is "suspended". For a multi-story building, meaning a building with more than one story, the use of a few common types of concrete suspended slabs are used (for more types refer to the section titled "Design" below):
  - Beam and block, also referred to as Rib and Block, are made up of pre-stressed lintels or beams and hollow blocks and are temporarily propped until set after 21 days. Mostly used in residential and industrial applications.
  - Hollow core slab is precast and installed on site with a crane.
  - In high rise buildings and skyscrapers, thinner, pre-cast concrete slabs are slung between the steel frames to form the floors and ceilings on each level. Cast in-Situ slabs which used in high rise buildings and huge shopping complexes as well as houses. These in-situ slabs are cast on site using shutters and reinforced steel. On the technical drawings, reinforced concrete slabs are often abbreviated to "r.c.c.slab" or simply "r.c.". Technical drawings are often created by structural Engineers who use software such as AutoCad or Revit structure.
2. Include:
  1. slabs of steel reinforced concrete
  2. Thinner slabs are called mud slabs, particularly when used under the main floor slabs or in crawl spaces.
3. Sources:
Design
1. A number of designs exist for suspended slabs to improve the strength-to-weight ratio. In all cases the top surface remains flat, and the underside is modulated:
  - A corrugated slab, is designed when the concrete is poured into a corrugated steel tray. This steel tray improves strength of the slab, and prevents the slab from bending under its own weight. The corrugations run side to side.
  - A ribbed slab, gives considerable extra strength on one direction.
  - A waffle slab, gives added strength in both directions and it looks hollow from bottom . Reinforcement design
  - A one-way slab needs moment resisting reinforcement only in its short-direction because the moment along long axes is so small that it can be neglected. When the ratio of the length of long direction to short direction of a slab is greater than 2 it can be considered as a one way slab. Long direction = ly Short direction = lx One way slab IF ly/lx > 2
  - A two-way slab needs moment resisting reinforcement in both directions. If the ratio of the lengths of long and short side is less than two then moment in both direction should be considered in design. Two way slab IF ly/lx < 2
2. Sources:
3. Link:
  1. Waffle Slab wiki: Waffle slab foundation
Construction of concrete slabs
1. A concrete slab may be prefabricated or prepared on site. Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. They may be pre-stressed (in the factory), post-stressed (on site), or unstressed. It is vital that the wall supporting structure is built to the correct dimensions, or the slabs may not fit. On-site concrete slabs are built on the building site using formwork - a type of boxing into which the wet concrete is poured. If the slab is to be reinforced, the rebars are positioned within the formwork before the concrete is poured. Plastic tipped metal, or plastic bar chairs are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. For a ground slab, the form-work may consist only of sidewalls pushed into the ground. For a suspended slab, the form-work is shaped like a tray, often supported by a temporary scaffold until the concrete sets. The formwork is commonly built from wooden planks and boards, plastic, or steel. On commercial building sites today, plastic and steel are more common as they save labour. On low-budget sites, for instance when laying a concrete garden path, wooden planks are very common. After the concrete has set the wood may be removed, or left there permanently. In some cases formwork is not necessary - for instance, a ground slab surrounded by brick or block foundation walls, where the walls act as the sides of the tray and hardcore acts as the base.
2. Sloped:
  1. http://www.concreteconstruction.net/how-to/construction/concrete-floor-slabs_o
3. on the ground vs within a building (stories/levels)
Commercial vs residential - any variation that has not been addressed?
1. Residential: http://www.diynetwork.com/how-to/rooms-and-spaces/floors/all-about-joist-and-concrete-floor-structures
2. Commercial (or rather heavy loads): http://www.concreteconstruction.net/how-to/construction/concrete-floor-slabs_o
Further Reading
1. Salvador, Mario. "Why Buildings Stand Up". Print.
2. Existing in Site: https://web.archive.org/web/20090117083125/http://www.concrete.net.au/publications/pdf/concretebasics.pdf

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