Contents:

**Reinforced Concrete Slab Design Guidelines**

**a) Effective span of slab: **

Effective span of slab shall be lesser of the two
- L = clear span + d (effective depth)
- L = Center to center distance between the support

**b) Depth of slab: **

The depth of slab depends on bending moment and deflection criterion. the trail depth can be obtained using:
- Effective depth d= Span /((L/d)
_{Basic}x modification factor) - For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%.
- The effective depth d of two way slabs can also be assumed using cl.24.1,IS 456 provided short span is <3.5m and loading class is <3.5KN/m
^{2}

Type of support |
Fe-250 |
Fe-415 |

Simply supported | L/35 | L/28 |

Continuous support | L/40 | L/32 |

**Or, the following thumb rules can be used:**

- One way slab d=(L/22) to (L/28).
- Two way simply supported slab d=(L/20) to (L/30)
- Two way restrained slab d=(L/30) to (L/32)

**c) Load on slab: **

The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m^{2}). Dead load = D x 25 kN/m

^{2}( Where D is thickness of slab in m) Floor finish (Assumed as)= 1 to 2 kN/m

^{2 }Live load (Assumed as) = 3 to 5 kN/m

^{2}(depending on the occupancy of the building)

**Detailing Requirements of Reinforced Concrete Slab as per IS456: 2000 **

**a) Nominal Cover: **

For Mild exposure – 20 mm
For Moderate exposure – 30 mm
However, if the diameter of bar do not exceed 12 mm, or cover may be reduced by 5 mm. Thus for main reinforcement up to 12 mm diameter bar and for mild exposure, the nominal cover is 15 mm.
**b) Minimum reinforcement:**

The reinforcement in either direction in slab shall not be less than
- 0.15% of the total cross sectional area for Fe-250 steel
- 0.12% of the total cross-sectional area for Fe-415 & Fe-500 steel.

**c) Spacing of bars:**

The maximum spacing of bars shall not exceed
- Main Steel – 3d or 300 mm whichever is smaller
- Distribution steel –5d or 450 mm whichever is smaller Where, ‘d’ is the effective depth of slab. Note: The minimum clear spacing of bars is not kept less than 75 mm (Preferably 100 mm) though code do not recommend any value.

**d) Maximum diameter of bar:**

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

**Basics of Reinforced Concrete Slab Design**

**Types of Design and Detailing Errors in Construction and their Prevention**

**Causes of Excessive Deflections in Reinforced Concrete Slabs**

**Types of Economical Floor Systems for Reinforced Concrete Buildings**