• Practically, it is a
common practice that if 𝐿/𝐵 > 1.5, design it
one way slab.

• If 𝐿_{𝑥}
> 3 𝑚: it is advisable to
provide a two-way slab.

• Common depth of slabs =
5”, 6” (125 mm, 150 mm); max=200 mm (for load = 5 𝑘𝑁/𝑚𝑚2
).

*L/D
***ratios:**

• One way S.S slab 𝐿/𝐷 = 20 × 𝑚. 𝑓 = 20 × 1.4 = 28 𝑓𝑜𝑟 𝑝𝑡 =
0.3%, 𝑚. 𝑓 = 1.4) . Adopt 𝐿 𝐷 = 25.

• One way continuous, above value (25) shall be
multiplied by 26/20 = 1.3 = 25 × 1.3 = 32.5. Adopt 𝐿/𝐷 = 32.

• Two way S.S slab 𝐿/𝐷 = 28 (for 𝐿𝑥 ≤
3.5𝑚 𝑎𝑛𝑑 𝐿. 𝐿 ≤ 3 𝑘𝑁 𝑚^{2} )

• Two way continuous slab 𝐿/𝐷 = 32 (for two-way
slab, shorter of the two spans be used to calculate 𝐿/𝐷 ratio

• **Common diameter of bars **=
8, 10, 12 mm. (dia. ≯ 𝐷/8)

• Approx. area of main
steel in slabs, 𝐴_{𝑠𝑡} = 𝑀𝑢/0.8𝑑.𝑓𝑦 (𝑀𝑢 =
0.138𝑓_{𝑐𝑘}𝑏𝑑^{2 })

**Theoretically,
calculated ****𝐴 _{𝑠𝑡}**

**is provided in the middle strip and min.**

**𝐴**

_{𝑠𝑡}

_{ }**is provided in edge strip. In practice, bars are uniformly provided spaced throughout spans in both directions.**

• Assume 𝐴_{𝑠𝑡} =
0.3 − 0.45% (one way slab)

• Assume 𝐴_{𝑠𝑡} =
0.2 − 0.3% (two way slab)

• Assume 𝐴_{𝑠𝑡} =
0.5% (one way continuous)

• Maximum area of main
steel in slab = 4% 𝑜𝑓 𝑏𝐷
(As per ACI).

• All top reinforcement of
slabs shall continue up to 𝐿/3
of span at both sides of C/L of wall or Beam.

• Corners free to lift:
cast over walls and no parapet above

• Roof slab with corner
held down is achieved by 230 mm **parapet wall**, 600 mm high and 2 m length on
either side of the corner

• Area of distribution steel = 0.12% 𝑜𝑓 𝑏𝐷
(For floor slab)

• Area of distribution
steel = 0.24% 𝑜𝑓 𝑏𝐷
(For roof slab)

• **Short span bars** are
provided in the bottom layer.

• If two different dia.
bars are used, provide larger dia. bars at the bottom layer.

• Due to openings in slabs,
area of steel interrupted be replaced by an equivalent amount, half of which
should be placed along each edge of the opening.

**Practical
considerations of one-way slab**

• Spacing shall be between **150-200 mm** (main bars)

• Spacing shall be between **150-300 mm** (distribution
bars)

• Max. Spacing of bars **3****𝑑** or **300 mm**,
whichever is less.

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