Staircase

INTRODUCTION Stairs: Stair can be defined as an arrangement of treads, risers, stringers, newel posts, hand rails and balustrades so designed and constructed as to provide an easy, safe and quick access to the users of different floors. It is series of steps arranged to connect the different floors of building and provided for an easy and quick access of different floors.

Staircase: Staircase is the room or enclosure of the building in which the stair is located. Materials used for construction of staircase are timber, stones, bricks, steel, P.C.C and R.C.C. The selection of material for construction depends upon the funds, availability of materials, and life expectancy of building, aesthetics and fire resistance quality expected. Stairs should be thoughtfully located carefully planned. They should be tastefully designed, serving purpose. They should be economical in construction. In residential houses, the staircases may be located at entrance or anywhere in house. But in public they should be centrally located easily. All stairs should be adequately light and properly ventilated.

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Different components of Staircase: First of all it is important to go over the different Basic Components of the staircase.

Baluster: The vertical members supporting the handrail are the Balusters. They are the light pillars.

Handrail

Baluster

Combined framework of handrail and baluster is known as

Balustrade. Flight: The series of steps without any platform or landing or break in their direction is Flight. A flight is a succession of steps uninterrupted by a landing.

Flight

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Tread: The upper horizontal part of the step on which foot is placed in ascending or descending a stairway is the Tread.

Risers: The vertical member between two treads is the Riser. It connects the back of one tread with the front of the next tread above it. It provides support to the tread. Rise: The vertical distance between the any two consecutive treads is the Rise.

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Nosing: The outer projected edge of the tread is Nosing. It makes the staircase easy to negotiate. For pleasing appearance it may have given rounded shape. An imaginary line connecting the nosing point parallel to slope of stair is known as the Line of Nosing.

Flier: The straight step having a parallel width tread is Flier.

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Run: The total length of stairs in a horizontal plane, including landing is the Run.

Scotia: The molding provided under the nosing to improve elevation of step is Scotia. It gives strength to nosing.

Nosing

Tread

Going Rise

Scotia

Riser

Going: The width of tread between two successive risers is Going. It is horizontal distance between the faces of any two consecutive risers.

Soffit: The underside of the stairs is Soffit.

Railing: The framework of enclosure supporting the handrail and serves, as safety barrier is the Railing

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Landing: The platform provided between two flights and which is used to change the direction of the stair is landing. A landing is the termination of one flight and the start of next. A landing extending to full width of staircase is half space landing and space extending only half across a staircase is called is quarter space landing.

Landing

Winder: The tapering steps used for changing the direction of stairs are the Winder. They are the steps that are narrower at one end than the other and are used in curves.

Header: The horizontal structural member supporting stair stringers or landing is the Header.

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Carriage: The rough timber supporting steps of wooden stairs is the Carriage.

String or Stringer: The sloping member, who supports the steps in stairs, is the String.

Handrail Baluster

Riser Newel post String Ficor level

Tread

Newel post: The vertical post place at the top and bottom ends of flight supporting handrails is Newel post.

Newels: The posts or columns used in some kinds of stairs at the turnings to connect the handrails and strings of adjacent flight are Newels. .

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Pitch or slope: The angle, which the line of nosing of stairs makes with the horizontal, is the Pitch or Slope.

Handrail: The protective bars placed at a convenient distance above the stairs for a handhold are the Handrail.

Angle post: The railing support or landings or other breaks in the stairs is the Angle post. If the angle post projects beyond the bottom of stringers, the arrangement details formed at the bottom of the post is known as the Drop.

Headroom: The minimum clear height or vertical space from a tread to overhead construction is the Headroom. It allows the majority of users to move freely, with risk of bumping their head against the ceiling. Example: Ceiling of next floor or piping.

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Here are two types of Balustrades shown below:

Handrail Baluster Top rail Panel

Handrail Iron Baluster Cement Lead Concrete stone Steps

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Requirements of good stairs: Stair is one of the means of vertical transportation between floors. It should be designed so as to provide easy, quick and safe mode of communication between floors. Following are the general requirements, which a staircase should fulfill: 1) Location:  It should be located as to provide easy access to occupants of building.  It should be so located that its well lighted and ventilated directly from exterior.  It should be so located as to have approaches convenient and spacious. 2) Width of stair:  It should be wide enough to carry the user without much crowd or inconvenience.  Width of stair depends up to its location in building and type of building itself.  If domestic building, a 90cm wide stair is sufficient while in public building, 1.5m to 1.8m width may be required. 3) Length of flight: From comfort point of view, the number of steps is not more than 12 and not less than 3. they may be between 9 to 11. 4) Pitch of stairs:  The pitch of the stairs should match with French theory: ‘the labour of moving vertically is about twice that of moving horizontally if the average human stride is taken as 23inches.  If rise and going are measured in inch units, the best pitch of stairs is that inclination which by twicing the rise and adding going equals 23.  When measured in cm units, a comfortable slope is achieved when twice rise plus going is equal to 60 approximately. Pitch should however, be limited to 30 degree to 45 degree. 5) Headroom: The clear distance between tread and soffit of flight immediately above it should not be less than 2.1m to 2.3m so that even a tall person can use the stair with same luggage on its head. 6) Balustrade: Open well stair should always be provided with balustrade, to provide safety to users. Wide stair should have hand rail to both the Sides. 7) Step dimensions:  The rise and going should be of such dimensions as to provide comfort to user,  Their proportion should also be such as to provide desirable pitch of stairs.  The going should not be less than 25cm, through 30cm is going is quite comfortable.

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8)

Rise should be between 10cm (for hospital) to 15cm. The width of landing should not be less than the width of stairs. Material of construction: The materials used for construction of stair should be such as to provide a. Sufficient strength. b. Fire resistance.

Classification of Stairs: We can classify the stairs on the basis of The shape of the stairs. The material used in construction of stairs.

Classification based on Shape of the stairs: First we will consider the classification based on the Shape of the Stairs. Stairs can be classified in two broad heads: 1. Straight stairs. 2. Turning stairs. 3. Continuous stairs.

1)

Straight stairs:

In this type the stair runs straight between the two floors. These are the stairs along which there is no change in direction on any flight between two successive floors. The straight stairs can be of the type: a) With a single flight. b) With a series of flights. c) Parallel stairs. d) Angle stairs. e) Scissors stairs. In some cases straight stairs can have a change in the direction at an intermediate landing. It is used for small houses where there are restrictions in available width. The stair may consist of either one single flight or more than one flight (usually two) with a leading, as shown:

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2)

Turning staircase:

The turning stairs can be again classified in following four types: a) Quarter turn stairs. b) Half turn stairs. c) Three quarter turn stairs. d) Bifurcated stairs. Each of the turning stairs is of three types: i.) Newel stairs. ii.) Well or open newel stairs. iii.) Geometrical stairs. A newel stair is the one that has a newel at the foot and head of each flight of the stair, and in which newels stairs, lateral space is left between the turning flights. In well or open newel stairs, lateral space is left between the turning flights. Open newel stairs presents the best appearance and are strong. The geometrical stairs have the string and handrails continuous and are set out in accordance with geometrical principles. They may be circular, spiral, helical or even elliptical. A newel may be introduced at the bottom and top of such a stair through it is not an essential part of the construction. Geometrical stairs require care and good deal of skill in their construction. They are not so imposing as the open newel type and are comparatively weak.

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Quarter turn stairs: This stairs are provided when the direction of the flight is to be changed by 90degree. The angle can be at the bottom, at the landing, or start at the bottom and continue uniformly to the top. This stair is the one change it’s direction either to the left or to the right, the turn being affected either introducing a quarter space landing by providing winders. The quarter turn stairs are of two types: i.) Newel quarter turn stairs. ii.) Geometrical quarter turn stairs. Now we will consider first type.

i.) Newel quarter turn stairs: These stairs have the conspicuous newel posts at the beginning end of each flight. At the quarter turn may either be quarter space landing there may be winders.

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ii.) Geometrical quarter turn stairs: In the geometrical stairs, the stringer as well as the handrail is continuous, with no newel post at the landing.

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a) Half turn stairs: The half turn stair is the one which has its direction reversed or changed for 180degree. Such stairs are quite common. These stairs can be of three types: i.) Dog legged or newel half turn stairs. ii.) Open newel half turn stairs. iii.) Geometrical half turns stairs. i.) Dog legged stairs: These are named so because, when viewed from the side elevation they have the appearance of the bend of a dog’s hind leg. They do not have a well separating the two flights, the outer strings and rails of the forward and backward flight are directly over one another. It comes 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 of two forms  With half space landing.  With quarter space landing and winders. Generally, former type (i.e. without winder) is more common. There is no space between the outer strings of two flights.

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ii.) Open newel half turn stairs: Open well or open newel half turn stair has a clear vertical space or well left between the progressive and retrogressive flights i.e. between the outer strings. Two newels are required instead of one as in the case of a dog legged staircase. 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 15cm (minimum) to 100cm. When the space left is more, a small flight containing two to four steps may be introduced at the turn, between the two quarter space landings. Otherwise for small width well a half space landing may be provided.

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iii.) Geometrical half turn stairs: The essential features of such stairs are that the stringers and the handrails are continuous, without any intervening newel post i.e. they have an open well similar to open newelled stairs but do not use a newel. The change of direction is curved, instead of boxed. The landings and winders have to be placed in the well as to produce agreeable curves in the strings and handrails.

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b) Three quarter turn stairs: These stairs are the combination of the first two types of turning stairs. Threequarter stairs have a flight of stairs that lead to a landing; the staircase then makes a 90degree turn up another flight, and then makes a 180-degree turn at a second landing i.e. a three quarter turn stair has its direction changed three times with its upper flight crossing the bottom one. It may either be newel type or open newel type. Such type of stair is used when the length of the stair room is limited and when the vertical distance between the two floors is quite large.

c) Bifurcated stairs: This type of stair is commonly used in public building at their entrance hall. The stairs has a wider flight at the bottom, which bifurcated into two narrower flights, one turning to the left and the other to right, at the landing. It may be either of newel type with a newel post or of geometrical type with continuous stringer and handrail.

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3) Continuous stairs: Continuous stairs are those, which do neither have any landing nor any intermediate newel post. They are, therefore, geometrical in shape. Continuous stairs may be of the following types: i.) Circular stairs. ii.) Spiral stairs. iii.) Helical stairs. We will see these types considering one by one. i.)

Circular stairs: These stairs, when viewed from above, appear to follow a circle with a single center of curvature and large radius. These stairs are generally provided at the rear of a building to give access for servicing at various floors. This stair is employed at a location where thee are space limitations. These are used as emergency stairs, and are provided at the backside of the building. All the steps radiate from a newel post in the form of winders. Hence, the stair is, therefore, not comfortable. These stairs can be constructed in stone, cast iron or R.C.C.

ii.)

Spiral stairs: These stairs are similar to circular stairs except that the radius of curvature is small and a center post may support the stairs. Overall diameter of such stairs may range from 1m to 2.5m.

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iii.)

Helical stairs: A helical stair looks very fine but its structural design and construction is very complicated. It is made of R.C.C. in which a large portion of steel is required to resist bending, shear and torsion. These stairs, when viewed from above, appear to follow a curve with two or more centers of curvature, such as an ellipse.

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Classification based on Material of construction: Stairs may be classified on the basis of material with which they are constructed. They are classified as a) Timber. b) Stone. c) Bricks. d) Steel. e) R.C.C. We will consider one by one.

a)

Timber Stairs:

Timber stairs are light in weight and easy to construct, but they have very poor fire resistance. They are used only for small residential buildings and for public buildings. Sometimes, fire resisting hard wood such as oak, mahogany etc. of proper thickness may be used. The timber used for the construction should be free from fungal decay and insect attack, and should be well treated before use. In timber stairs the strings are the supports for the stair and act as inclined beam, spanning between the floor and the landing. For additional support a bearer or a carriage may be placed under the treads. The normal practice is to provide one bearer, for a 90cm wide staircase and an additional bearer for every 40cm of width. The thickness of strings may be 3cm to 5cm and depth may be between 25cm to 40cm.

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 Steps of timber stairs: The thickness of tread of a timber stair should not be less than 32mm (1 ¼ inch) and that of riser 25mm (1mm). Timber risers and tread joined by tongue and grooved joints. The joints are nailed or screwed. The nosing of the step should not project beyond the face of the riser for more than the thickness of the tread. Scotia blocks may be provided to improve the appearance of the steps.

 Landing: A landing is constructed of tongued and grooved boarding on timber joists, which are supported on walls. In the case of half space landing, a timber joists known as timber is placed across the full width of the staircase. In the case of quarter space landing, a timber joist known as pitching piece, is placed in the wall of one end and housed with the newel at the other end.

 Stringer: These are the inclined beams of timber of 30mm to 50mm thickness and 25cm to 40cm deep, supported on newels, trimming joists or pitching pieces. These stringers are of four types: i. Cut string. ii. Housed string. iii. Rough string iv. Wreathed string. We will consider one by one.

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ii.) Cut string: A cut string has its upper surface having carriages or houses accurately cut to receive the treads and risers; such strings improve very much the appearance of a stairs. However, it’s lower edge is kept parallel to cut made, it becomes weak. iii.) Housed string: A housed or closed stringer has its top and bottom edges parallel to the pitch of the stair. Grooves are cut on its inside to receive the treads and risers of the steps which are generally nailed, glued and wedged to the stringers. The grooves or housings are tapered so that wedges may be driven below the treads and risers, thus forming a tight joint on the upper surface. These wedges are best made from hard wood; they are dipped in glue before driving these. To add rigidly, blocks are glued between the string and the treads and risers. iv.) Rough string: A rough string is an intermediate bearer provided for wider steps. The carriage giving support to the treads and risers has rough brackets under the tread. v.) Wreathed string: A wreathed string is a curved or geometrical stair string, which may be either of cut or closed type.

 Landing: A landing is constructed of tongued and grooved boarding on timber joists, which are supported on walls. In the case of half space landing, a timber joists known as timber is placed across the full width of the staircase. In the case of quarter space landing, a timber joist known as pitching piece, is placed in the wall of one end and housed with the newel at the other end.

b)

Stone stairs:

Stone stairs are widely used at places where ashlar stone is readily available. Stone stairs are quite strong and rigid, though they are very heavy. Stone used for construction of stairs should be hard, strong and resistant to wear; stones are fire resistant also. The simplest form of stone stairs is those supported on both the ends, though an open well staircase can also be built. Dog legged stairs; with cantilevered spandril steps are also constructed of sand stone, such as the type available at Jodhpur. Stone stairs may have following types of steps: i. Rectangular steps with rebated joints. ii. Spandril steps. iii. Tread and riser steps. iv. Cantilevers tread steps. v. Built up steps. We will consider one by one.

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i.)

Rectangular steps: These are the simplest type, prepared from rectangular blocks of stone ashlar. The steps are arranged with the front edge of one step resting on the upper back edge of the step below, with rebated joint cut into it.

ii.)

Spandril steps: These steps are nearly triangular in shape so as to get a plain soffit. At the end, each step is built in the wall. Such steps give pleasant appearance. The soffit may either be plain, broken or moulded. As shown in figure steps are rebated to fit on the ones below.

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iii.) Slab tread and riser steps: In this type, flag stone slabs are used as tread and risers, similar to the timber steps. The stone slab risers and treads may be connected through dowels. The thickness of stone slab may vary from 5cm to 8cm.

iv.) Cantilever tread slab steps: In this type, the steps are formed by treads only, made of thick stone slabs, without any riser. The tread slab is fixed at one end into the wall, and acts as cantilever. The steps may either be rectangular or triangularly shaped.

v.) Built up steps: These steps use treads and risers in the form of thin sawn stone or marble slabs, placed over brick or concrete steps. The thickness of stone slab may vary from 2cm to 5cm.

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c)

Brick stairs:

Brick stairs are not very common except at the entrance. However, brick stairs of single straight flight are often made in village houses. The stair consists of either solid wall, or also, arched openings may be left for obtaining storage space. The brick steps need frequent maintenance. Hence these may be faced with stone slabs. Alternatively, these steps may be cement plastered at the top of treads and side of risers.

d)

Metal stairs:

The stairs of mild steel or cast iron are used only as emergency stairs. They are not common in residential and public buildings, though they are strong and fire resistant. This is because they are not good looking and also, they make lot of noise when used by users. They are commonly used in factories, godowns, workshops etc. In its simplest form, a metal stair consist of rolled steel stringers (mostly channel sections) to which angle irons are welded or riveted and steel plates are used as treads. Another form of metal stairs commonly used is the spiral stairs.

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e)

R.C.C. stairs:

R.C.C. stairs are the one, which are widely used for residential, public and industrial buildings. They are strong, hard wearing and fire resisting. These are usually cast-in-situ, and a variety of finishes can be use on these. Based on the direction of span of the stair slab, concrete stairs may be divided into two categories: i.) Stair with slab spanning horizontally. ii.) Stair with slab spanning longitudinally. We will consider one by one. i.)

Stair with slab spanning horizontally: In this category the slab is supported on one side-by-side wall or stringer beam and on the other side by a stringer beam. Sometimes, as in the case of straight stair, side wall on one side of each flight and the common newel on the other side between backward and forward flights may support the slab horizontally. In such case the effective span L is the horizontal distance between centre to centre of the supports. Each step is designed as spanning horizontally with the bending moment equal WL2 /8, where W is the uniformly distributed load per unit area, on the step, inclusive of the Self-weight. Each step is considered equivalent to a rectangular beam of width b (measured parallel to the slope of the stair).

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ii.)

Stair with slab spanning longitudinally: In this category, the slab is supported at bottom and top of the flight and remains unsupported on the sides. Each flight of the stair is continuous, and is supported on the beams at top and bottom or a landing. In the later case, the landings also become the part of slab. Dog legged stairs are typical example of this type. The main reinforcement is provided parallel to the direction of the flight and the distribution reinforcement is provided along the width of the slab. Sometimes, especially for wider stairs, a central stringer beam spanning between the end walls or column is provided on which the stair slab (waist slab) is supported; the waist slab is designed as slab cantilevering both the sides of stringer beam. The stringer beam itself is designed as a T-beam.

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1.R.C.C. helical stair: R.C.C. can be used in constructing stair of any geometrical shape. Figure shows helical stair, which is cast-in-situ. A large amount of steel reinforcement is used to resist bending moment. Shear force and torsional moment. The continuous slab varies in thickness from top to bottom less at top and increasing at the bottom layers in each: i.) Continuous bars running the length of the spiral. ii.) Cross or radial bars. iii.) Diagonal bars laid tangential in two directions to the either inner curve.

2. Precast concrete stairs: Precast concrete units are now-a-days available for the construction of concrete stairs of various shapes. The three common types of precast units are: i.) Rectangular cantilever steps. ii.) Spandril cantilever steps. iii.) Sector-shaped cantilever units. The latter type is used for the construction of open riser spiral stair.

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BIBLIOGRAPHY

 “BUILDING CONSTRUCTION” by Dr.B.C. Punmia.  “BULIDING CONSTRUCTION” by Mr.Bindra and Arora

INTERNET-LINKS  www.rintel.com  www.arcways.com  www.rona.ca  www.southernstairs.com

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