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.
General Design Consideration for Design of staircase:
Dwelling Houses and Factories Tread = 250 mm
Public Building Tread = 270 mm
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
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
Thichness of waist
Assume Span/Effective depth = 30
so depth = Effective depth – cover – bar dia/2
General Consideration for 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)
Mu = WL²/10
0.138Fck*bd² = Mu
now this depth should be less than depth taken.
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
Check for shear
V = WL/2 KN/m
τ v= V/(1000*depth) N/mm² < 0.28 N/mm²
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