Detail of Construction of Stair.
Definition:
A stair may be defined as series of steps suitably arranged for the purpose of connecting different floors of a building. It may also be defined as an arrangement of treads,risers,strigers,newel posts, handrails and baluster.
Classification of stair:
Stair can be classified in three broad heads-
1) Straight stairs
2) Turning stairs
- Quarter turn stairs
- Half turn stairs (dog-legged and open well stair )
- Three-quarter turn stairs
- Bifurcated stairs
Each of the turning stairs are of two types-
-Newel stairs
-Open/Well
-Dog-legged
-Geometrical stairs
3)Continuous stair
- Circular
-spiral
-Helical
Straight stairs:
Straight stair runs straight between the two floors.It is used for small houses where there are restriction in available width. The stair may consist of either one single flight or more than one flight with a landing.
Quarter turn stairs-
A quarter turn stair is one which changes its direction either to the left or to the right ,the turn being to the left or right , the turn being affected either by introducing a quarter space landing or by providing winders. Quarter turn stair are two types-
a) Newel quarter turn stairs.
b) Geometric quarter turn stairs
These the stairs have conspicuous newel posts at the beginning and end of each flight. At the quarter turn there may either be quarter space landing or there may be winders.
b)Geometric quarter turn stairs
In geometric stairs the stringer as well as the hand rail is continuous , with no newel posts at the landing
.
Half turn stairs-
Half turn stair is one which has its direction reversed or changed for 180w . Such stair are quite common. These may be three types:
a) Dog-legged stair.
b) Open newel half turn stair.
c) Geometric half turn stair.
a) Dog-legged stairs.
This name is given because of its appearance in sectional elevation. Incomes under the category of newel (or solid newel ) stairs in which newel posts are provided at the beginning and end of each flight. These may be two forms :
1) With half space landing
2) With quarter space landing lining and winders.
Generally the former type is more common is shown in the figure. There is no space between the outer strings of the two flights.
b) Open newel half turn stair
Open well or open newel half turn stair has a space or well between the outer strings. This is the only aspect in which it differs from the dog-legged stair. The additional width is required between the two flights, the space between the two strings may vary from 6″ (minimum) to 40″.
c) Geometrical half turn stair:
The essential feature of such stairs are that the stringers and the hand rails are continuous without any intervening newel post. These may be either with half space landing or without landing.
Bifurcated stairs
This types of stair commonly used in public building at their entrance hall. The stair has a winder flight at the bottom, which bifurcates into two narrower flights, one turning to the left and the other to the right, at the landing. It may be either of newel type with a newel post as shown in the figure.
Continuous Stair:
Continuous stair are those which do neither any landing nor any intermediate newel post. They are following types-
- Circular stair
- Spiral stair
- Helical stair.
Technical Term Used in Stair:
Step: It is the portion of a stair which permits ascent or decent. Tread: It is the upper horizontal portion of a step upon which the foot is placed. Riser: It is the vertical portion of a step providing a support to the tread. Landing: It is the level platform at the tread or bottom of a flight between the floors. Flight: Unbroken series of steps between landing. Going: It is the horizontal distance between two successive faces. Noising: It is the projected part between two successive riser faces. Sofia: It is the underside of a stair. Line of noising: It is an imaginary line touching the noising of each tread and is parallel to the slope of the stair. Pitch or slope: It is the angle which the line of noising of stair makes with horizontal. Newel post: It is the vertical member which is placed at the end of flight to connect the hand of strings and hand rails. Baluster: It is the vertical member of wood and metal supporting the hand rail.Dimension of step:
Rise = 5.5-6 inchGoing = 12 inch as standard.
2 ×(rise in inch) +(going in inch ) =23inch (rise in inch)+(going in inch)=16-18 inch (rise in inch)×(going in inch)=64-72 inch2Requirements of a good stair:
Location: It should be located as to provide easy access to the occupant of the building. It should be so located that its well lighted and ventilated directly from the exterior. It should be so located as to have approaches convenient and spacious. Width of stair: It should be wide enough to carry the user much crowed or inconvenience. Width of stairs depends up to its location in the building and type of building itself. Length of flight: From comport point view, the number of steps are not more than 12 and not less than 3. Head room: The clear distance between tread and soffit of the flight immediately above it should not be less than 6'10" to 7'6" so that even a tall person can use stair with some luggage on its head. Pitch of the stair: The pitch of the stair should match with the French theory; the labour of moving vertically is about twice that of moving horizontally, if the average human stride is taken as 23 inches. Slope should however be limited to 30° to 45°.
Balustrade: Open well stair should always be provided with Balustrade to provide safety to the user. Wide stair should have hand rail to the both sides. Materials of construction: The material used for the construction of the stair should be such as to provide sufficient strength and fire resistance. 
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