Requirement Of good Stair & Type |Civil Engineer must Know
Stairs give access from floor to floor. Stairs consists of a number of steps arranged in a single flight or more number of flights.
The requirement of good stairs are describe as following :
- Tread : Horizontal projection of a step in a stair case is called tread.. In residential buildings tread provided is 250 mm while in public buildings it is 270 mm to 300 mm.
The following empirical formula is used to decide rise and tread:
2 R + T > 550 mm but < 700 to 600 mm
where R is riser in mm and T is tread in mm.
- Number of Steps in a Flight: Maximum number of steps in a flight should be limited to 12 to 14, while minimum is 3.
- Riser : Riser provided should be uniform. It is normally 150 mm to 175 mm in residential buildings while it is kept between 120 mm to 150 mm in public buildings. However in commercial buildings more rise is provided from the consideration of economic floor area.
- Width : 0.9 m in residential buildings and 1.5 m to 2.5 m in public buildings.
- Hand Rails: Hand rails should be provided at a convenient height of a normal person which is from 850 mm to 900 mm.
- Head Room: Head room available in the stair case should not be less than 2.1 m.
Types of Stairs
Reinforced concrete stairs are very commonly used in all types of buildings.There are many type of stairs are describe as following :-
- Straight stairs
- Dog legged stairs
- Well or open-newel stairs
- Geometrical stairs
- Spiral stairs
- Turning stairs.
Straight Stairs: If the space available for stair case is narrow and long, straight stairs may be provided. Such stairs are commonly used to give access to porch or as emergency exits to cinema halls. In this type all steps are in one direction. They may be provided in single flight or in two flights with landing between the two flights
Dog Legged Stairs: It consists of two straight flights with 180° turn between the two. They are very commonly used to give access from floor to floor.
Well or Open-newel Stairs: It differs from dog legged stairs such that in this case there is 0.15 m to 1.0 m gap between the two adjacent flights.
Geometrical Stair: This type of stair is similar to the open newel stair except that well formed between the two adjacent flights is curved .The hand rail provided is continuous.
Spiral Stairs: These stairs are commonly used as emergency exits. It consists of a central post supporting a series of steps arranged in the form of a spiral. At the end of steps continuous hand rail is provided. Such stairs are provided where space available for stairs is very much limited
Turning Stairs: Apart from dog legged and open newel type turns, stairs may turn 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.