Can you tell me types of slabs? And how can we design them?
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Flat slab – Flat slab is minimum 8″ or 0.2m.
Conventional slab – conventional slab is 4″ or 10cm. 5″ to 6″ inches
Hollow core ribbed slab
Pitch roof slab
Slab with arches
Post tension slab
Pre tension Slab
Low roof slab
Grads Slab/ Slab on grade
a) 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
b) Depth of slab:
The depth of slab depends on bending moment and deflection criterion. the trail depth can be obtained using:
Type of support
Fe-250 – L/35
Fe-415 – L/28
Fe-250 – L/40
Fe-415 – L/32
Or, the following thumb rules can be used:
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/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 RCC 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
c) Spacing of bars: The maximum spacing of bars shall not exceed
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.
Narrowly and basically categorising, there are only two types of slabs : one way slabs and two way slabs (depending on the length/width ratio). Now, they both can be of several types including :
The design begins basically with the calculation of loads and their distribution. For this it is best to take loads as point loads and follow Pigued method (pronounced : pee-joh). This will give us the maximum loads and moments that we need the slab to service in worst cases. Taking a suitable factor of safety we can proceed to design the slabs as per the standard design codes (IS 456 (2000) in India).
there is two type of slab one is one way slab & another one two way slab ,two way slab further divided into two categories one is simply supported two way slab & another one restrained. Design is available in IS CODE:456