Following are the RCC Slab Design and Detailing guidelines

Reinforced Concrete Slab Design Guidelines

1- Effective span of slab

Effective span of slab shall be lesser of the two

1- L = clear span + d (effective depth)

2- L = Center to center distance between the support

2- Depth of slab

The depth of slab depends on bending moment  and deflection  criterion.  the trail depth can be obtained using

1- Effective depth d= Span /((L/d)Basic x modification factor)

2- For obtaining modification factor, the percentage of steel for slab can be assumed from 0.2 to 0.5%.

3- The effective depth d of two way slabs can also be  assumed using cl.24.1,IS 456 provided short span is <3.5 m and loading class is <3.5 KN/m2

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

1- One way slab d=(L/22) to (L/28).

2- Two way simply supported slab d=(L/20) to (L/30)

3- Two way restrained slab d=(L/30) to (L/32)

3- Load on slab

The load on slab comprises of Dead load, floor finish and live load. The loads are calculated per unit area (load/m2).

Dead load = D x 25 kN/m2 ( Where D is thickness of slab in m)

Floor finish (Assumed as)= 1 to 2 kN/m2

Live load (Assumed as) = 3 to 5 kN/m2 (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

1- 0.15% of the total cross sectional area for Fe-250 steel.

2- 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

1- Main Steel – 3d or 300 mm whichever is smaller

2- 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.

Share this
Leave a Reply

Your email address will not be published. Required fields are marked *