There are two types of bars present in the slab
1- Main bars
2- Distribution bars (bars provided against shrinkage and temperature)
Maximum spacing Between Individual Bars
1- The maximum diameter of the bar used in the slab should not exceed 1/8 of the total thickness of the 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, the diameter of the bar, the thickness of the slab, effective depth and spacing are co-related.
Effective depth = depth of slab – clear cover- half of the diameter of the 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 the 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)