Concrete slabs in buildings

[edit] Introduction

A slab is a structural element, made of concrete, that is used to create flat horizontal surfaces such as floors, roof decks and ceilings. A slab is generally several inches thick and supported by beams,columns, walls, or the ground.

Concrete slabs can be prefabricated off-site and lowered into place or may be poured in-situ using formwork. If reinforcement is required, slabs can be pre-stressed or the concrete can be poured over rebar positioned within the formwork.

There are several different types of slab, including:

[edit] Flat slab

This is a typically a reinforced slab supported directly by columns or caps, without the use of beams. This type of slab is generally easy to construct and requires little formwork.

[edit] Conventional slab

This type of slab is supported with beams and columns, with the load transferred to those elements. A conventional slab is classified as either:

• One-way: Supported by beams on two opposite sides, carrying the load along one direction.
• Two-way: Supported by beams on all four sides, carrying the load along both directions.

[edit] Hollow core ribbed slab

This type of slab has longitudinal voids/cores running through it, which decrease the weight of the slab, as well as the amount of concrete required. They can also function as service ducts. This type of slab is generally reinforced with longitudinal rebar, and can achieve long spans, making it suitable for office buildings, multi-storey car parks, and so on.

[edit] Waffle slab

This type of slab contains square grids with deep sides, resembling a waffle shape, often used where large spans are required without the interference of columns. Waffle slabs can be capable of supporting a greater load than conventional slabs.

[edit] Solid slab raft

This is a type of shallow foundation, typically formed by a reinforced concrete slab that covers a wide area, often the entire footprint of a building. It spreads the load imposed by a number of columns, walls, and so on, over a large area, and can be considered to ‘float’ on the ground in a similar way to a raft floating on water. It is often used for lightly-loaded buildings on weak or expansive soils such as clays or peat.

For more information, see Types of raft foundation.

[edit] Composite slab

Composite slabs are typically constructed from reinforced concrete cast on top of profiled steel decking, (re-entrant or trapezoidal). Slabs are most commonly made of concrete because of its mass and stiffness which can be used to reduce the floor's deflections and vibrations, and achieve the necessary fire protection and thermal storage. Steel is often used as the supporting system underneath the slab due to its superior strength-weight and stiffness-weight ratio and ease of handling.

For more information, see Composite slab.

[edit] Find out more

[edit] Related articles on Designing Buildings Wiki

• Building foundations.
• Cast-in-place concrete.
• Cellular raft foundation.
• Concrete.
• Domestic floors: Part 1: Construction, insulation and damp proofing.
• Floating floors in buildings.
• Footings.
• Pad foundation.
• Strip foundation.
• Types of floor.
• Types of raft foundation.