Staircase design, Analysis Modeling. Know Importance, Staircase design Plans. Stairs is a set of steps which give access from floor to floor from ground level. The room or enclosure of the building, in which stair is located is known as the staircase. Staircase provides access between floors in multi-storey buildings upto top roof and are a path by which fire can spread from one floor to another. It consists of a flight of steps (stairs) and one or more intermediate landing slabs between the floor levels. Therefore it must be enclosed by fire resisting walls, floors, ceilings and doors.
Staircase Plan, Design Concrete Construction, Calculations
Now many various Different types of staircases can be made by arranging stairs and landing slabs. Check Out Beautiful Staircase designs here. Staircase, thus, is a structure enclosing a stair. Steps or Stairs are essential for any construction, not only as a way to mediate between two levels, but also to facilitate the access within a building. The stairs must meet the following quality requirements: strength and stability, fire safety, safety in use, acoustics protection. Hygiene, human health and environmental protection requirements can be considered complied with if the construction and finishing materials emit no pollutants.
It must be designed to carry certain loads, which are similar to those used for design of the floors. Stairs may be constructed of Timber, Bricks, Stone, Steel or Reinforced Cement Concrete. The design of staircase, therefore, is the application of the designs of the different elements of the staircase.
Staircase Designs, Sizes, Definitions
Steps: A stair is to be designed to span a large vertical distance by dividing it into
smaller vertical distances, called steps.
StairCase: The room or enclosure of the building, in which stair is located is known as staircase.
Riser: It is a vertical portion of a step providing support to the tread. The vertical distance between two successive steps is termed as riser
Flight: This is an unbroken series of steps between landing.
Noising: In some cases the tread is projected outward to increase the space. This projection is designated as nosing
Scotia: It is a moulding provided under the nosing to provide strength to nosing.
Thread: The horizontal top portion of a step where foot rests is known as tread.
Balanced treads: Treads that go follow a curved path, with tread edges that converge to centers of different radius. In a drawing plan, each tread has a different shape
Going: Going is the horizontal projection between the first and the last riser of an inclined flight
Pitch or Scope: It is the angle which the line of nosing of the stair makes with the horizontal.
Soffit: it is the underside of a stair.
Winders: Winders are steps that are narrower on one side than the other. They are used to change the direction of the stairs without landings. A series of winders form a circular or spiral stairway.
handrail: A rail fixed parallel above the pitch line at the sides of a stair.
Headroom: It is the clear vertical distance between the tread and overload structure.
Newel: A vertical post which might provide support for either the handrail, or support for the upper end of an outer string.
Total length : The circulation space between the wall and the railing
Stringer: The lateral or central beam going along the flight or stairs bearing all its weight.
High risers: A staircase with risers of height between 17.6 and 22.5cm
Low Risers: A staircase with risers of height lowers than 16.5cm
Abrupt staircase: A staircase that has treads with the width between 22.6 and 30
Construction of Staircase in mind of Mechanical resistance and stability, Safety in use, Fire safety and Noise protection as basic requirement conditions.
The respective dimensions of tread and riser for all the parallel steps should be the same in consecutive floor of a building.
Stair should always provided with balustrade. The width of landing should not be less than width of stair.
The rise and going should be of such dimensions as to provide comfort to users.
The minimum vertical headroom above any step should be 2 m. The rise should be between 10 to 15 cm. Generally, the number of risers in a flight should be restricted to twelve.
The material should have fire resistance and sufficient strong.
Stairs located near the main entrance to the building. Height of headroom should not be less than 2.1 to 2.3 m
It should be wide enough to carry the user without much crowd on inconvenience.
Easy access from all the rooms without disturbing the privacy of the rooms.
Good light and ventilation should be available.
Pitch should be limited to 30o to 45o
The number of steps should not be more than 12 & less than 3 from comfort point of view.
The “eye” of the staircase the free space bound by the inner parts of flight of stairs
Staircase Minimum Dimensions, Design Conditions
The rise and going should be of such dimensions as to provide comfort to users.
The going should not be less than 25 cm, though 30 cm going is quite comfortable.
The width of landing should not be less than width of stair
The rise should be between 10 to 15 cm.
Relationship between riser and tread can be shown as 2R+T=63cm
•Convention centers, cinema,Theaters: R=16cm
•Schools, hospitals, Office buildings R= 17cm
•Residential Buildings R=18cm
Min.Tread width (no side walls) =60cm
One side wall = 70cm
Two side walls = 80cm
Treads can be made out of reinforced concrete, metal, wood or glass. They are often used in staircases in residential or commercial buildings (showrooms, small shops) due to their unique design .They are not recommended for buildings used by great crowds of users or for evacuation staircases.
Types of Staircase
Type of Staircase mainly according to the shape of the flight of stairs. There can be stairs with flights, stairs are straight, curved, L-Shaped, balanced. The type of stair, shape must be choosen not only comforming to the available space.
– Quarter Turn
– Half Turn (Dog-Legged & Open well Staircase)
– Three-Quarter Turn Staircase
– Bifurcated Staircase
– Circular Staircase
– Spiral Staircase
Straight staircase is recommended. if space available go with formal simple traditional design.In this type all steps are in one direction. it is Simplest form of stair arrangement Consists of one straight flight of stairs linking two levels. The width and the length of the landings should be equal (max.120cm). it’s highly reccomended to orient the tread after the axis of the staircase in order to avoid a lack of precision when finishing corners, especially if the staircase is enclosed within a shaft or has rectangular shape.
Quarter Turn Staircase
Well shaped like Dog-Legged Staircase. it consists of two straight flights with 180° turn between the two. very commonly used to give access from floor to floor. Two short flights with a half space landing between them. 180 degree staircase can be designed for different spaces. It’s not supposed to be a safety evacuation staircase ,since it serves only one circulation flux.It’s the most economical way to occupy space because the treads also replace the landing
Apart from Traditional style staircases, comparing with Dog legged and open newel type turns looks better in various forms. They depend upon the available space for stairs. Quarter turned, half turned with few steps in between and bifurcated stairs are some of such turned stairs.
Spiral type of staircases are commonly used as Emergency exists. it takes less space and consists of a central post supporting a series of steps arranged in the form of a spiral. Such stairs are provided where space available for stairs is very much limited. At the end of steps continuous hand rail is provided.
Designing the staircase depends on many factors, Natural place space, the staircase is going to be situated, the size of hole in the slab and type of building. basic requirement load-bearing capacity various for residential, commercial and industrial uses.
Usual slopes for the flight of stairs.The relation between the length of
the tread (l) and the height of the riser (h).
The relation between the length of the tread (l) and the height of the riser( h)
defines the slope of the flight of stairs.
2h + l = 63 ft.
where h= riser heigt I= tread
for example I tread=26 cm
The Minimum optimal height
2h=63-27 = 34
h= 34/2 = 17
The width of the ramp is depending upon various factors. It’s an important factor one must consider to allow a smooth flow of circulation. The width of the flight of stairs represents the circulation space between the wall and the rail or between 2 rails. Minimum range of depth plans. Depending on the type of building and the number of floors, code regulations demand certain minimum widths for smooth flows of circulation .Various type of building has different width sizes. check out some of below.
Industrial buildings; 1.20 Width Main Staircase 1:10 Width Secondary Main Staircase
Residential buildings maximum 2 floors: 1.05 Primary, 1.05 Secondary
Residential buildings 3-5 floors: 1.15 Main, 1.00 Secondary
Buildings with overcrowded halls: 1.70 Main, 1.20 Secondary
Design of StairCase
General Design Consideration for Design of staircase:
Step 1: Tread
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
Design of staircase civil engineeirng
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
Thickness 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
Step 3: 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)
Step 4: Bending Moment
Mu = WL²/10 0.138Fck*bd² = Mu
now this depth should be less than depth taken.
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
Step 6: Check for shear
V = WL/2 KN/m
τ v= V/(1000*depth) N/mm² < 0.28 N/mm²
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