Design of Staircase according to IS 456:2000

Design of staircase

General Guidelines For Design of staircase:

The following are some of the general guidelines to be considered while Design of staircase:

• The respective dimensions of tread and riser for all the parallel steps should be the same in consecutive floor of a building.

• The minimum vertical headroom above any step should be 2 m.

• Generally, the number of risers in a flight should be restricted to twelve.

• The minimum width of stair should be 850 mm, though it is desirable to have the width between 1.1 to 1.6 m. In public building, cinema halls etc., large widths of the stair should be provided.

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General Design Consideration for Design of staircase:

Step 1:

Tread

Dwelling Houses and Factories Tread = 250 mm

Public Building Tread = 270 mm

Riser

Public Building Riser = 150mm

Factories Riser = 190 mm

Residential Building = 160 mm

These values are not fixed, but used for reference purpose.

Tread is also know as Going (G)

> we can also check design parameter according to a popular formula given below

It should follow 2R+G>550 mm and 2R+G<700 mm

i.e. 550mm<2R+G<700mm

It also depend on (i) the Span of staircase and (ii) Height of Building

(i) How to calculate Effective Span

Effective Span –  –   –   –   –   –   –   –   –   –     Clause 33.1, Page 61, IS 456:2000

In case 1:

If value of x and y is less than 1(one), then Effective span = x+y+Going length

If value of x and y is greater than 1(one), then Effective span = 1+1+Going length 

so Effective span should not be more than (Going length + 2)

In case 2:

Effective Span = center to center distance of beam

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Thichness of waist

Assume Span/Effective depth = 30

so depth = Effective depth – cover – bar dia/2

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Step 2:

General Consideration for Load

Live Load

Residential Building load (without overcrowding) = 2 KN/m2

Public Building Load (including overcrowding) = 5KN/m2

Dead Load calculation

Dead load per meter square of Horizontal Span = weight of Rectangle slab + Weight of Triangle portion

Dead Load /m2 = [W1B+RT/2]25/G

here Length= B, Width = 1 meter and Height= Waist(thickness of slab)

 

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Step 4:

Bending Moment

Mu = WL²/10

0.138Fck*bd² = Mu

now this depth should be less than depth taken.

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Step 5:

Area Of Steel 

Mu = 0.36Fck*x/d (1-.416 x/d)bd²

Here we get value of (x/d)

So Lever Arm Z = d(1 – 0.146 x/d)

here a shortcut that we can take lever arm 85 to 95 percent of effective depth by previous experience.

Now Ast = Mu/(0.87 *Fy *Z )  mm² per meter width

so number of bar = area of steel ÷ spacing

Distribution steel = 0.12% of width and overall depth = 0.12WidthDepth/100

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Step 6:

Check for shear 

V = WL/2 KN/m

τ v=  V/(1000*depth) N/mm² < 0.28 N/mm²

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Step 7:

Check For Deflection

Percent of steel = 0.48

L/d = 26 For continuous [ Fig 4, Page 38, IS 456]

Fs = No of bar*spacing/area of steel

so F = 1.2

so Allowable L/d = 1.2*26

we assume L/d = 30< 31.2 Hence Ok