Important Notes On Slab (Spacing, Effective Depth Etc)


Important Notes On Slab:

There are two types of bars present in the slab.


  • Main bars
  • Distribution bars (bars provided against shrinkage and temperature)

Maximum spacing Between Individual Bars:

1) The maximum diameter of bar used in slab should not exceed 1/8 of the total thickness of slab.

2) For main bars, maximum spacing is restricted to 3 times effective depth or 300 mm whichever is smaller.

3) For distribution bars, the maximum spacing is specified as 5 times the effective depth or 450 mm whichever is smaller.

Hence, diameter of bar, thickness of slab, effective depth and spacing are co-related.

Effective depth = depth of slab – clear cover- half of diameter of bar

Minimum Distance Between Individual Bars:

Minimum Distance Between Individual Bars  & main reinforcing bars shall usually be not less than the greatest of the following:

The following shall apply for spacing of bars:

1) The diameter of the bar if the diameters are equal,

2) The diameter of the larger bar if the diameters are unequal and

3) 5 mm more than the nominal maximum size of coarse aggregate.

Clear cover (Nominal Cover) shall be kept in mind while calculating the above parameters.

Source: IS-456 (2000)

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