Stairs may be made
from various materials like timber, stones, bricks, steel, plain or reinforced
concrete. The selection of the type of material to be used depends upon the
aesthetical importance, funds available, durability and fire resisting
qualities excepted.
LOCATION OF STAIRS
The location of stairs
in a building requires consideration. In the advent of fire or any such
calamity, stairs provide the only means of communication and such they are so
located as to serve the purpose for which they are provided. In public building
it should be located near the main entrance and in residential building it
should be placed centrally so as to provide easy access from all the rooms and
to maintain privacy at the same time.
TECHNICAL TERMS
Steps: A portion of a stair way comprising the tread and riser which permits
ascent and descent from one floor to another.
Tread: The horizontal upper part of a step on which foot is placed in ascending
or descending stairway.
Riser: The vertical portion of a step providing support to the tread.
Flight: A series of steps without any platform, break or landing in their
direction.
Landing: A platform or resting place provided between two flights. A landing
extending right across a stair case is termed as half space landing and the one
extending only half across a stair case is called quarter space landing.
Nosing: The outer projecting edge of a tread is termed as nosing. Nosing is
normally rounded to give good architectural effect to the treads and makes the
stair case easy to negotiate.
Scotia: It is a moulding provided under nosing to beautify the elevation of the
step.
Line of Nosing: It is an imaginary line touching the nosing of each tread and
is parallel to the slope of the stair.
Filler: It is a straight step having a parallel width of tread.
Soffit: It is the under surface of a stair.
Slope: It is an angle which the line of nosing of the stair makes with the
horizontal.
Strings or Stringers: These are the sloping wooden members providing support for
the steps. For stairs of average width, the stringers are usually provided one
outside and the other adjacent to the wall.
Handrails: It is provided to render assistance in negotiating a stair
way. It is supported on balustrades and usually run parallel to the slope of
the stair.
Balustrade: It usually consists of a row of balusters surmounted by a
rail and is provided to perform the function of a fence or guard for the users
of the stair way.
Head Room: It is the clear vertical distance between the tread of a step
and the soffit of the flight or the ceiling of a landing immediately over it.
Spandrel: It is the triangular framing under the outside string of an
open string stair.
REQUIREMENTS OF A GOOD STAIR
A well planned and
designed stair should provide an easy, quick and safe mode of communication
between the various floors. The general requirements of a good stair may be
divided into the different heads, described below:
2.Width of a Stair: Width of a stair with the situation and the purpose for which
it is provided. In public buildings, where there is a regular traffic or people
using the stair way, its width should be sufficient while in a residential
building it may be just the minimum. The usually adopted average value of the
stair width for public and residential building is 1.8 m and 90 cm.
respectively.
3. Length of Flight: For the comfortable ascent of stair way the number of steps
in a flight should be restricted to a maximum of 12 and a minimum of 3.
4. Pitch of Stair: The pitch of long stair should be made flatter by introducing
landings to make the ascent less tiresome and less dangerous.
5. Head Room: The head room or the clear distance between the tread and the soffit of the flight immediately above it should not be less than 2.14 m.
6. Materials: The stair should preferably be constructed of materials which
possess fire resisting qualities.
7. Balustrade: The open well stairs should be provided with balustrade so as
to minimise the danger of accident.
8. Winders: The introduction of winders in stair should be avoided as far
as possible. They are liable to be dangerous and involve extra expense in
construction. They are difficult to carpet and are especially unsuitable for
public buildings. However, where the winders cannot be dispensed with, they
should preferably be provided near the lower end of the flight. Thus instead of
quarters space landing, three winders may be used and for a half space landing,
five winders or four radiating risers may be adopted.
CLASSIFICATION OF STAIRS
STRAIGHT STAIR:
The most obvious use of the straight stair is to form an access to entrance, porch or portico. Straight stairs cannot be avoided in places, where the stair case hall is long and narrow and the possibility of any other form of stair may not be practically possible. In this form of stair, all the steps rise in the same direction. If the ascending is steep, the straight flight may be broken at an intermediate landing.
DOG LEGGED STAIR
It consists of two straight flights of steps with abrupt turn between them. Usually, a level landing is placed across the two flights at the change of direction. This type of stair is useful where the width of the stair case hall is just sufficient to accommodate two widths of stair.
This is similar to the open newel stair with the difference that the open well between the forward and the backward flight is curved. In this form of stair, the change in direction is obtained through winders.
Circular stair is commonly provided at the backside of a building for rendering access to its various floors for service purposes. The circular stairs are commonly constructed in R.C.C., cast iron or stone. In this form of stairs all the steps radiate from a newel post or wel hole, in the form of winders.
It consists of two or more straight flights arranged in such a manner that a clear space called a ‘well’ occurs between the backward and the forward flights. If the width of the stair case hall is such that it becomes difficult to accommodate the number of steps in two flights, without exceeding the maximum allowable limit of steps in each flight, a short flight of 3 to 6 steps may be provided along the width of the hall.
Timber is mainly used for stair construction where fire
resistance is not of much consideration. Timber stairs are cheap, easy in
construction and maintenance and light in weight. Timber stair constructed from
fire resisting hard wood, like oak, teak, mahogany etc., using minimum
thickness of various members as 5 cm. is found to serve the requirements of a
fire resisting to a great extent. The various components of timber stairs are
described below:
Steps: The thickness of tread should not be less than 32 mm and that of the risers as 25 mm. it is a common practice to adopt the thickness of tread as 38 mm. The risers and the treads are connected by tongue and grooved joints and the joints are nailed or screwed. The nosing of the step should not project beyond the riser for a distance more than the thickness of the tread. The nosing may be suitably finished by scotia piece.
Stringers: As described earlier, stringers are employed to provide
support for the steps. Strings are inclined wooden members 32 to 50 mm thick
and 25 to 38 cm deep. They are supported on newels, trimming joists or pitching
pieces. Stringers may be broadly classified into four main types:
1.Cut String
2. Housed and closed
string
3. Rough String
4. Wreathed string
1.Cut String: It is stringer with its upper surface having carriages or houses accurately cut to receive the treads and risers and the lower edge being parallel to the pitch of the stair. It is considered that the appearance of stair is improved by use of cut string, but it has the disadvantage of weakening the string as deep cuts have to be made in it.
2. Closed String: It is a stringer having its top and bottom edges parallel to
the slop of the stair. It has grooves cut on its inside to receive the treads
and risers of the steps. The treads and risers are usually nailed, glued and
wedged to the stringer.
3. Rough String: Rough strings are introduced in wider stairs for the purpose of rendering intermediate support to the steps.
4.
Wreathed String: It is curved or
geometrical stair string. It may be of cut or closed type.
Winders: In narrow stairs, the treads of winder steps are supported on risers
which act as cantilever beams fixed in the staircase wall. In such cases, the
riser should be of sufficient thickness to perform the function of a cantilever
beam. At its free end, the cantilever riser beam is housed into the newel post.
For wider stairs the winders are supported by means of bearers built into the
wall at one end and framed and housed into the newels a the other. The back of
the bearer is rendered flush with that of the riser immediately over it.
Landings: These may be constructed of tongued and grooved boarding
supported on joists. The arrangement for supporting the boarding differs with
type of landing.
In case of straight
stairs, newels are carried down to the ground floor and bearers are provided
from the newels up to the staircase wall. The landing joists are provided
between the bearers which in turn support the boarding.
In forming quarter
space landing, a timber joist, known as ‘pitching piece’, is built within the
wall at one end and housed with the newel at the other. Depending upon the type
of newel, the pitching piece may be supported as a beam or it may act as a cantilever
beam fixed in the staircase wall. In case where the pitching piece acts as a
cantilever beam, it should be strengthened by means of a bracket below it. Pitching
pieces support the ridging joist to which the landing boarding is fixed.
For forming a half space landing, wooden joist known as trimmer is fixed across the width of the staircase. Landing joists or bridging joists are tennoned into the trimmer at one end and are supported on the staircase wall at the other end.
Reinforced concrete
stairs predominate the stairs made from wood, stone or metal. This is because
of the various advantages R.C.C has over other materials. Reinforced concrete
is perhaps the most suitable of all the said materials for the construction of
the stairs. R.C.C, stairs can be moulded in any desired form to suit the
requirements of the architect.
Advantages:
· They have requisite fire resisting
qualities to a great extent.
·
They
are durable, strong, pleasing in appearance and can be easily rendered
non-slippery.
·
They
can be designed for greater widths and longer spans.
·
They
can be easily cleared.
·
The
cost of maintenance is almost nil.
· In a framed structure of reinforced
concrete, R.C.C., stair in perhaps the only choice.
Reinforced concrete
stairs can be pre cast or cast in situ. To change their appearance, R.C.C.
stairs are often covered with thin slabs of stone, marble tiles or with
terrazzo finish. In order to prevent the nosing of the step getting cracked or knocked
off.
Design Principle: The choice of the type of stair to be adopted depends very
much upon the size of the staircase hall and the loading condition. In short,
the design of the reinforced concrete stairs may be broadly divided into
following categories.
· R.C.C. steps cantilever out from the
stair case wall and acting both as supporting beam and stair.
·
R.C.C.
steps spanning between two inclined R.C.C. beams.
· An inclined slab of the full width of the stair and supported between beams or landing slabs at either end and the steps cast monolithic with the inclined slab.
METAL STAIRS
They are usually
fabricated from steel and cast iron and their use in generally restricted to
factories, godowns etc. In its simplest form, a metal stair consists of steel
stringer to which steel angles are riveted r welded and metal treads are
provided over then.
Advantages
1.Extreme Versatility: A staircase can be custom designed and constructed
into a variety of shapes and sizes. Common metal staircase includes stainless
steel, aluminium, and wrought iron. Each of these metal options offers unique
aesthetic and construction benefits, and our team works closely with each
customer to determine the type of metal that is the best fit or the project.
2. Minimal Maintenance: In addition to design versatility, metal stairs are
known for requiring very little maintenance. Unlike wood, metal stairs do not
require sealant., varnish or paint to maintain an outstanding appearance.
3. Maximum Durability: Metal staircases require very little upkeep, and they
are truly built to last. Highly functional and resistant to extreme temperature
changes and humidity fluctuations, metal staircases are an ideal choice- either
indoors or out.
Below, a spiral metal
staircase withstands the elements- wind, sea and sand- outside of a coastal
home.
For many years, builders, designers, architects and homeowners have turned to metal staircases to enhance residential and commercial spaces.
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