What is a floor slab and why detailing is required for a slab?

Yes floor slab, we normally don’t give so much attention to design a floor slab. Floor slab is also called as base slab. But in some cases the floor slab can be more complex, where the ground water level is higher and thus water proofing is required and also in cases where the strength of sub soil is very low.

Before going into the design of floor slab we should have an idea about the type of soil. You should decide which type of foundation is best suited for the type of soil and structure. In most of the cases the floor slabs are precast slabs.

You can check the design procedure for one way and two way slabs

A floor slab is

  • A flat slab of thickness less than 100 mm supported by the subsoil.
  • A slab which requires steel reinforcement some times temporary to support the concrete.
  • A base slab which should have a protective layer basically a water proofing layer.
  • A pre-cast slab used should be properly checked and the strength should be ensured before using.

Detailing of a slab design

Clear cover

Clear cover is the distance measured from the exposed concrete surface to the nearest surface of reinforcing bars. The requirement as per the code :

  • Mild exposure – 20 mm
  • Moderate exposure – 30 mm
  • Severe exposure – 45 mm
  • Very severe exposure – 50 mm
  • Extreme exposure – 75 mm

Minimum reinforcement

The reinforcement in either direction of the slab shall not be less than

  • 0.0015 of the total cross sectional area for Fe 250 steel
  • 0.0012 of the total cross sectional area for Fe 415 steel.

Maximum spacing of bar

It is specified for the purpose of controlling crack width and shall not exceed.

  • Main steel – 3d or 300 mm which is smaller.
  • Distribution steel – 5d or 450 mm whichever is smaller

Minimum spacing of bar

It is specified for the purpose of proper compaction of concrete so that the aggregate present in concrete should not get stuck in the mesh. It shall not be less than 75 mm.

Maximum diameter of bar

The maximum diameter of bar in slab, shall not exceed D/8, where D is the total thickness of slab.

Slab design

  • RCC Slab Design is a free app for designing one way and two way reinforced concrete slab systems as per Indian Standards.
  • RCC Design and detailing could be performed for ten different boundary conditions specified in IS456:2000
  • Option to save the design projects in local storage.
  • Detailed calculation steps presented for verification and validation.

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