Steps involved in design of a one way slab | IS 456: 2000?

In present scenario it is very easy to design a one way slab. As in most of the cases we use some third party commercial software to design the structure. Even then I believe for a civil engineer it is very much important to be aware about the different steps involved in designing the one way slab as per the IS specification.

You can check this post to know about one way slab.

Steps to design a one way slab

Step 1 : Determine the effective span of the slab (lx by ly)

  • Assume an effective depth (d) on the basis of span to effective depth ratio (Table 1).
  • Then compute the value of overall depth (D).
  • Overall depth D = d + clear cover
  • Clear cover depends on the exposure condition (for mild exposure, clear cover = 20 mm and for moderate exposure, clear cover = 30 mm ).
  • Effective span (l) l = lx + width of support or lx + d —– A lesser of these two
Type of slabSpan <= 10 mSpan > 10 m
Cantilever beam7 deflection should be calculated
Simply supported2020 x 10 / span
Table 1 as per IS 456:2000

Step 2 : Analysis – Calculate the moment

  • Consider the various loads due to
    • Self weight
    • Dead Load
    • Live load
  • Calculate the total load and factored load (1.5 * Total load)
  • Calculate the bending moment

$$ M_u = \frac{W_u \times l^2 }{8} $$

Step 3 : Determine the area of reinforcement ( Ast )

  • Compute the value of constant R using : $$ R = \frac{M_u}{bd^2}$$
  • Compute the value of Ast using the formula : $$ \frac{p_t}{100} = \frac{A_{st}}{bd} = \frac{f_{ck}}{2 f_y} [1 – (1 – 4.598 \frac{R}{f_{ck}})^{0.5}] $$
  • Calculate the number of bars and decide the placements of bars in layers for the main steel.
  • Provide the minimum reinforcement as the distribution steel.

Step 4 : Check

The minimum reinforcement in each direction should not be less than

  • 0.15% of the Ast for Fe-250 steel
  • 0.12% of the Ast for Fe-415 & Fe-500 steel.

The max. spacing of bars should not be more than

  • 3d or 300 mm whichever is smaller for main steel
  • 5d or 450 mm whichever is smaller for distribution steel

You can design the one way slab using our android application.

Slab design

  • RCC Slab Design is a free app for designing one way and two way reinforced concrete slab systems as per Indian Standards.
  • RCC Design and detailing could be performed for ten different boundary conditions specified in IS456:2000
  • Option to save the design projects in local storage.
  • Detailed calculation steps presented for verification and validation.

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