Chpater 21 STAIRS AND ELEVATORS – Building Construction Materials and Techniques

21

STAIRS AND ELEVATORS

21.1 INTRODUCTION

A stair is a sequence of arrangement of steps which is provided as a means of easy ascent and decent between the floors or landings.

Stairs are of different types which are designed and used based on the location and usage. Stairs are provided in almost all types of buildings starting from residential building to multi-storeyed buildings.

Different materials are used for the construction of stairs, viz., stone, wood, brick, metal and concrete (both plain and reinforced).

In order to have a comfortable climb and descend, proper design has to be stipulated as regards to size of stairs, slope, landing space, etc.

Other modes of transportation between floors are lifts, ramps and moving stairs.

In this chapter, salient features of stairs and other transportation facilities are discussed.

21.2 COMPONENTS OF A STAIRCASE

The space occupied by the stairs is called a staircase or stairwell. Various components of a stair are shown in Fig. 21.1 and also defined below.

1. Baluster

It is a vertical member supporting the handrail.

2. Flight

It is a series of steps without any break such as a platform, landing, etc.

3. Tread

It is an upper horizontal portion of a step used to keep the foot while ascending or descending.

4. Riser

It is a vertical portion of a step which provides support to the tread.

5. Step

It is a portion of the stair comprising of tread and riser.

Figure 21.1 Components of a staircase

6. Rise

It is a vertical length between the upper faces of any two consecutive steps.

7. Landing

It is a flat platform provided between the flights.

8. Winders

These are the tapering used for a change of direction in a stair.

9. Soffit

It is the under surface of a stair.

10. Going

It is the horizontal projection of the flight.

21.3 REQUIREMENTS OF A GOOD STAIR

A well-planned and designed stair should be comfortable, quick, safe and easy to use. Different aspects which are to be considered in the planning and design of stairs are discussed below.

21.3.1 Location

The location of stairway should be so chosen such that sufficient ventilation and light should be available. If it is feasible, it may be located centrally so as to be of easily accessible from different parts of a building.

21.3.2 Width of Stair

Width of a stair, in general, should be adequate for the users without much crowd. It depends very much on the type of building and the number of users. In general, 1.0 m width is adopted for residential building and about 1.5 m width for public buildings.

21.3.3 Pitch of a Stair

The pitch or slope of a stair should prevent undue exortion to the user and at the same time there should not be any waste of space. Normally the slope of a stair should not exceed 40° and should not be flatter than 20°.

21.3.4 Length of a Flight

In order to make the ascend comfortably, the stairway should not have steps more than 12 and a minimum of 3.

21.3.5 Headroom

The headroom or the clear distance between the tread and the soffit of the flight immediately should be adequate. This should be at least 2.14 m.

21.3.6 Materials of a Stair

Construction of a stair should be carried out with sound and fireproof materials. Further, it should be adequately durable so as to have long life as that of the other materials used for the construction of the building.

21.3.7 Landing

The width of landing should not be less than the width of a stair.

21.3.8 Winder

As far as possible, the introduction of a winder should be avoided. They are liable to be dangerous. If it is inevitable, it may be provided near the lower end of a flight. Thus instead of quarter-space landing, three winders may be used. Similarly for half-space landing five winders or four radiating risers may be adopted.

21.3.9 Step Proportions

All the risers and treads should be of uniform dimensions. The steps should neither be too wide or too short. Further high rise may cause inconvenience and fatigue to the user.

The following empirical rules may be followed:

  1. Rise + Tread : not < 40 and not > 45
  2. 2 Rise + Tread : not < 58 and not > 63
  3. (Rise) × (Tread) : not < 400 and not > 500

For residential buildings, the common size of step is 15 × 28 cm. Rise greater than 20 cm and tread less than 22 cm should not be used. In general, (2 Rise + Tread) approximately equal to 60 will give a comfortable flight.

21.4 TYPES OF STAIRS

Different types of stairs which are in general use are discussed below.

21.4.1 Straight Stairs

In this type of stairs, there is no change in direction of any flight between successive floors. These stairs may have (i) straight run with a single flight or (ii) straight run with a series of flights with one or two landings in between. If the staircase hall is long and narrow, only straight stairs can be thought of (Fig. 21.2).

Figure 21.2 Straight stairs

21.4.2 Quarter-turn Stairs

This type of stairs is preferred when there is a need for change of direction by 90°. The change in direction may be accompanied by providing either by introducing quarter-space landing or by providing winders (Fig. 21.3).

Figure 21.3 Quarter-turn stairs

21.4.3 Dog-legged Stairs

In this type of stairs, the direction of flight is changed through 180° by introduction of landings and or winders. A half-space landing may be used. It is also called as dog-legged stairs. This type of stair is useful where the width of the stair-case is just sufficient to accommodate two widths of stair (Fig. 21.4).

Figure 21.4 Dog-legged stairs

21.4.4 Three-quarter Turn Stairs

This type of stairs is provided with change in directions by 270°. That is, the direction is changed three times. In this case, an open-well is provided (Fig. 21.5). It is also called open newel stair.

Figure 21.5 Three quarter-turn stairs

21.4.5 Geometrical Stairs

These stairs have no newel post and may be of any geometrical shape. Here the strings and hand rails are continuous and are set out in accordance with geometrical principles. Thus these stairs are also called as continuous stairs. They may be winding stairs, half-turn stairs (with landing or newels) and spiral stairs (Fig. 21.6).

Figure 21.6 Geometrical stairs

21.4.6 Bifurcated Stairs

In these stairs, the bottom flight is wide which is divided into narrow flights from either side of the landing (Fig. 21.7). This type of stair is provided in modern public buildings.

Figure 21.7 Bifurcated staircase

21.4.7 Multiple Flight Stairs

It is an open-well type of stair which has four flights each with flight turn of 90°. It has an excellent view in a building (Fig. 21.8).

Figure 21.8 Multiple flight stairs

21.5 MATERIALS USED FOR STAIRS

Timber, stone, brick, steel, plain concrete and reinforced cement concrete (RCC) are in general the materials used for construction of stairs. They are accordingly classified based on the type of material used for construction.

21.5.1 Timber Stairs

Timber or wooden stairs are generally used for residential buildings because of its light weight and less usage. Further, this is preferred in areas where abundant wood is available. They are easy to construct and maintain. But they are liable to fire accidents. Timber should be free of fungal decay, insect attacks and other defects.

A typical detail of a wooden stair is shown in Fig. 21.9.

Straight flight stairs, half-turn stairs and open-well stairs may be constructed of wood.

Figure 21.9 Typical details of a wooden stair

21.5.2 Stone Stairs

Stone stairs are heavy and need substantial supports. They are preferred for outside stairs and for threshold, approach to basements, heating chambers, etc. Due to regular use, the steps become slippery and dangerous.

Stones are in general hard, durable and weather resistant. They are widely used at places where ashlar stones are readily available. Different types of stone steps adopted are as follows:

  1. Rectangular steps
  2. Spandril steps
  3. Built-up steps

1. Rectangular Steps

Typical rectangular steps are shown in Fig. 21.10.

Figure 21.10 Typical rebated stone steps

In rectangular steps, the lower edge of one step is supported on the top back edge of the other. In order to strengthen the joint, rebated or checked joints are used. To provide a better appearance, the front edges have moulded noses.

2. Spandril Stone Steps

Here the steps are cut so as to provide a plain soffit. In general, these steps are nearly triangular in shape except at the ends which are built into the wall. This arrangement is used where the headroom is desired. The soffit affords a nice appearance and the weight of steps is also reduced.

Figure 21.11 shows spandrel steps with different soffit arrangements.

Figure 21.11 Spandril steps with different soffit arrangements

3. Built-up Steps

In built-up steps, the tread and riser of each step are made of thin swan slabs similar to timber steps. The stone slab treads and risers are connected by dowels. In case the treads are supported at the ends only, then the thickness of the tread should be more than 5 cm. The stone slabs are placed over concrete or brick steps. This type of steps will give an ornamental look where granite or marble stones are used. Figure 21.12 shows a built up steps at an entrance.

Figure 21.12 Built-up step at entrance

21.5.3 Brick Stairs

Brick stairs may be of solid masonry construction or provided with arches in the lower portion. When arches are provided, the total masonry work is reduced. This space may be used as a cupboard or as a passage. Here the treads and risers are generally made equal to length of bricks and height of two layers of bricks respectively. Figure 21.13 shows a brick stair. The treads and risers of brick stair are finished with suitable flooring material.

Figure 21.13 Brick stair with arch opening

21.5.4 Steel Stairs

Steel stairs are of special type which are fire resistant and are preferred in factories, workshops, godowns, etc. These are made of pre-stressed sheet steel. The steel sheets are formed into risers or pans to which the treads are inserted. The treads and risers are supported on angles which are in turn connected to the stringer. Treads may be of stone-concrete composition or metal.

21.5.5 Concrete Stairs

Plain concrete stairs are used in place of stone stairs these days. They are mostly used for the entrance to the buildings. These steps are mostly of spandril type and are supported as in the case of stone stairs.

Now-a-days, RCC stairs are mostly used in all types of buildings. Reinforced concrete stairs derive a lot of advantages compared to other types. They are as follows:

  1. It can be easily moulded into any required geometrical shape.
  2. It has high resistance to wear and fire better than any other material.
  3. It needs less bulky sections, thereby more headroom may be attained.
  4. It is less noisy.
  5. It gives highly attractive appearance with appropriate finishes.
  6. It can be kept clean.
  7. It can be easily rendered non-slippery.
  8. It can be designed to accommodate greater widths and longer spans.

A typical RCC slab stair is shown in Fig. 21.14.

Figure 21.14 Typical RCC slab stair

Concrete stairs may be spanning horizontally or longitudinally. Stairs spanning horizontally are supported at each side by walls, stringer beams, or at one side by wall and at the other side by a beam. Stairs spacing longitudinally span between supports at the bottom and top of the flight and remain unsupported at the top and the bottom.

21.6 DESIGN PRINCIPLES OF STAIRCASE

The following provisions are to be adopted as per IS: 456–2000 in the design of staircases.

21.6.1 Dead Loads

Dead loads to be considered for staircase design comprise of self-weight of the waist slab, treads and risers, and self-weight of finishes. Finishes include hand rail, balusters and newel post.

21.6.2 Live Loads

For residential buildings, a uniformly distributed load of 2–3 kN/m2 may be adopted depending on the users. For public buildings, a uniformly distributed load of 5 kN/m2 is specified.

21.6.3 Effective Span of Stairs

  1. When the flight of the stair is supported at the ends of landing beams, the effective span is taken as the projected horizontal distance between the centre lines of landing beam.
  2. When the stairs are not provided with stringer beam, then the effective span shall be taken as the following horizontal distances:

    (i) Where supported at top and bottom risers by beams standing parallel with the risers, the distance centre-to-centre of beams.

    (ii) Where spanning on to the edge of a landing slab, which spans parallel with the risers (Fig. 21.15) a distance equal to the going of the stairs plus at each one, either half the width of landing or 1 m, whichever is smaller.

    (iii) Where the landing slab spans in the same direction as the stairs, they shall be considered as acting together to form a single slab and the span is determined as the distance centre-to-centre of the supporting beam or walls, the going being measured horizontally.

Figure 21.15 Effective span for stairs supported at each end by landings (Source: IS: 456–2000)

21.6.4 Rise and Tread

Following are the norms for the size of rise and tread:

The following guidelines may be followed while deciding the size of rise and tread of a stair:

  1. 400 mm < (Rise + Tread) < 450 mm
  2. 580 mm < (Rise + Tread) < 630 mm

21.6.5 Distribution of Load

Distribution of load for two conditions are given below:

  1. In the case of stairs with open-well where spans partly crossing at right angles occur, the load on areas common to any two such spans may be taken as one-half in each direction (Fig. 21.16).

    Figure 21.16 Distribution of loads on stairs (Source: IS: 456–2000)

  2. Where flights or landings are embedded into walls for a length not less than 110 mm and are designed to span in the direction of the flight a 150 mm strip may be deducted from the loaded area and the effective breadth of the section increased to 75 mm for the purpose of design (Fig. 21.17).

    Figure 21.17 Loading on stairs built into walls (Source: IS: 456–2000)

21.7 RAMPS

Ramps are sloping surfaces that join two floors. These are provided where large numbers of people or vehicles or equipment have to be moved from floor to floor. Now-a-days, ramps are specially provided in all public places like hospitals, railway stations, etc., for movement of aged and physically challenged persons. Multi-storey car parks that are generally provided at the heart of the cities have ramps.

Ramps should be provided with a non-slippery surface. They occupy much larger space than stairs. It should be provided with a uniform sloping surface.

Ramps may be located either externally from the general building line or internally (i.e., inside the building). Based on the intended use, it can be located internally or externally. For movement of heavy equipment’s, it may be preferred outside.

The ramp size evidently depends on its use. However, the following factors are taken into account in designing a ramp:

  1. The general slope of ramp is 15%. But a slope of 10% is preferred.
  2. The width of ramp depends on the use. Minimum width of pedestrian ramps is 75 cm and a minimum slope of 1 in 10 cm is adopted.
  3. Level landings with a length of at least 1.1 m in the direction of travel should be provided at door openings and where ramps change slope or direction abruptly.
  4. The shape of ramp need not be straight but it may be of any geometrical shape.
  5. Ramp and landing should be designed for a live load of at least 21.2 kg/cm2.
  6. Powered ramps may operate on slopes up to 8° at speeds up to 60 m/min. and/or slopes up to 15° at speeds up to 47 m/min.
  7. For carrying car and other machinery, a minimum of 4 m and a maximum width of 8 m is provided. A gentle slope of 1 in 10 cm is given. Here a straight or curved type can be provided.
  8. For external location, ramps are constructed with two retaining walls with rising tops on either side. The central portion is suitably filled with rising surface.
  9. If the ramp is provided inside the building, it may be designed as an inclined RCC slab or as slab supported as columns or stingers.
  10. Ramp surfaces may be rough cement or granolithic surface. Surface patterns or transverse grooves may be formed to improve slip resistance.
21.8 ELEVATORS

Buildings which are having more than four storeys are provided with elevators or also called as lifts. The function of an elevator is to provide vertical transportation of passengers or freight. The elevators may be of two types, viz., electric traction elevators or hydraulic elevators.

For a low-rise freight service, hydraulic elevators are provided which can rise up to about six storeys. It is also used for low-rise passenger service. Electric traction elevators can be provided for all rise buildings and structures. According to building regulations, it is mandatory to provide lift or ramp in all public buildings.

21.8.1 Components of an Elevator

Components of an elevator are the following:

  1. Lift car is the one which is to move on guide rails.
  2. A machine room with electric motor, winding machine and other necessary machines.
  3. Suspension rope to hold and move the car.
  4. Counterweight on pulleys to balance the car with about 50% of maximum live load.
  5. Buffers for the car in the lift pit floor. For low velocity lifts, spring buffers are used and oil buffers for velocity lifts.
  6. Special landing facility for entry and exit.
  7. Capacity of a passenger lift is based on the weight of person taken as 68 kg.

21.8.2 Structural Component of an Elevator

Civil engineering construction components needed for an elevator operation are given below:

  1. A lift well of suitable size. It is usually extending up to 1600–2000 mm below the bottom landing.
  2. At every floor level for entry of people an opening of height of 2 m is to be provided.
  3. An upper machine room on the top of the lift to suit the lift size is chosen.

21.8.3 Types of Elevators

Elevators are used for different purposes and accordingly they are classified as follows:

  1. Passenger lifts
  2. Goods lifts
  3. Hospital lifts
  4. Service lifts
  5. Fireman’s lifts

Separate specifications are available for each type of elevator. The relevant IS code has to be referred for specifications.

21.9 ESCALATORS

These stairs are also known as moving stairs or even moving flights. By a revolving drum, the escalator is kept in motion. A few steps at top and bottom are kept level through moving individually. A person has to occupy a step (preferably the first step) of the escalator for the upward or downward motion.

Essential features of the escalators are discussed below.

21.9.1 Essential Parts of Escalator

An escalator comprises of three parts, viz., steel trussed framework, hand rails and an endless belt with steps. Accurately arranged tracks are attached to the steel trusses and the steps move on these tracks.

21.9.2 Speed and Slope of Escalator

Speed of the escalator is normally 45 cm per second. The pitch or slope of the inclined bridge is kept at 30°. The moving stair is in the form of an inclined bridge between two successive floors.

21.9.3 Location of Escalator

It is necessary to make a careful study of flow of traffic before deciding the position of the moving stair. In a new structure the escalator has to be fixed at a position where the traffic is likely to be the heaviest.

21.9.4 Design Aspects of Escalator

The anticipated load on the escalator has to be properly assessed before design. The main factor which affects the design is the floor-to-floor height. The stair way should be kept independent by providing a structural framework around the stair well. The structural frame is designed to take care of the load of floor, hand rail, etc.

21.9.5 Installation

The various parts of the moving stair are fabricated in a workshop and installed at the location. Adequate care has to be exercised while installing each part. This arrangement ensures smooth working of the morning stair. Generally, escalators are fixed in pairs, one for upward movement and the other for downward movement. The escalators may be positioned diagonally opposite to each other or parallel to each other.

Example 21.1

The staircase room available in a residential building is 1.4 m × 4.8 m. The head room available is 3.2 m. Draw a lay-out plan of the stairs.

Solution:

As the space available is only 1.4 m, the width of staircase be taken as 1.4 m and no turn can be provided. Further the length of the stair is 4.8 m only and a landing can not be provided. Thus a straight-flight staircase be provided.

A rise of 20 cm is assumed

No. of risers (R)

∴ No. of treads (T )

Width of tread is assumed as 25 cm

Space for passage = 4.8 – 3.75 = 1.05 m

The layout is shown in Fig. 21.18

Figure 21.18

Example 21.2

A dog-legged staircase has to be provided in an office building. The staircase room is of 3.0 m × 6.0 m. The distance between the floors is 8.5 m. Design the stair-case and draw the lay-out plan.

Solution:

Width of stair is assumed as 1.4 m. As the width of the staircase is 3 m, a half space landing is provided with two flights. The width of landing is made equal to width of the stair.

Height of each flight

A riser of 15 cm is assumed

No. of risers (R)

Exact rise of each step

No. of treads to be provided in each flight

T = R – 1 = 12 – 1 = 11

Tread is taken as 30 cm

Here 15 cm × 30 cm step satisfies all the rules.

Space left for passage = 6 – 3.6 = 2.4 m.

The lay-out plan is shown in Fig. 21.19.

Figure 21.19

Example 21.3

It is intended to provide a suitable staircase for a hospital which consists of ground floor and first floor. The details are

Staircase room size = 6.0 m × 4.3 m

Height of each floor = 3.5 m

Thickness of floor slab = 15 cm

Width of stair = 140 cm

Provide a provision for lift.

Solution

An open-newel stair may be designed. The space of the well may be utilized for provision of a lift.

As in Example 21.2, adopt a rise of 15 cm and a tread of 30 cm.

Then,

Provide 10 steps in the first flight, 5 steps in the second flight and 8 steps in third flight.

Figure 21.20 shows the lay-out plan of the staircase.

Figure 21.20 Staircase 600 cm × 430 cm

SALIENT POINTS
  1. A stair is defined as a sequence of steps which are provided to ascend or descend between the floors or landings.
  2. The space occupied by the stairs is called a staircase or stairwell.
  3. A well-planned and designed stairway should be comfortable, quick, safe and easy to use.
  4. The location of a stairway should be so chosen such that sufficient ventilation and light should be available.
  5. Width of a stair in general, should be adequate for the users without much crowd. It depends on the type of building and the number of users.
  6. Pitch or slope of a stair should prevent undue exhaustion to the user and at the same time there should not be any waste of space.
  7. In order to make the ascend comfortable, the stairway should not have steps more than 12 and a minimum of 3.
  8. The headroom or the clear distance between the tread and the soffit of the flight immediately should be adequate. This should be at least 2.14 m.
  9. As far as possible, the introduction of a winder should be avoided. If it is inevitable, it may be provided near the lower end of a flight.
  10. All the risers and treads should be of uniform dimensions. The steps should neither be too wide or too short. The following empirical rules may be followed:

    (i) Rise + Tread: not < 40 and not > 45

    (ii) 2 Rise + Tread: not < 58 and not > 63

    (iii) (Rise) × (Tread): not < 400 and not > 500

  11. In straight stairs there is no change in direction of any flight between successive floors.
  12. Quarter-turn stirs are preferred when there is a need for change of direction by 90°.
  13. In dog-legged stairs the direction of flight is changed through 180° by introduction of landings and or winders.
  14. Three-quarter turn of open newel stairs are provided with change in direction through 270°.
  15. Geometrical stairs also called as continuous stairs have no newel post and may be of any shape.
  16. In Bifurcated stairs the bottom flight is wide which is divided into narrow flights from either side of the landing.
  17. Multiple flight stairs is an open-well type of stairs which has four flights each flight turn 90°.
  18. Timber, stone, brick, steel, plain concrete and RCC are in general the materials used for construction of stairs.
  19. Timber or wooden stairs are generally used for residential buildings because of its light weight and less usage.
  20. Stone stairs are preferred for outside stairs and for threshold, approach to basements, heating chambers, etc.
  21. Brick stairs may be of solid masonry construction or provided with arches in the lower portion.
  22. Steel stairs are of special type which are fire resistant and are preferred in factories, workshops, godowns, etc.
  23. Plain concrete stairs are used mostly for the entrance of the buildings. These steps are of spandrel type.
  24. RCC stairs are used mostly in all type of buildings now-a-days.
  25. Design principles to be considered are: Dead load, Live load, Effective span of stairs, Rise and Tread proportion and Distribution of load.
  26. Ramps are sloping surfaces which join two floors. These are provided where large numbers of people or vehicles or equipment have to be moved from floor to floor. Ramps are specially provided in all public places like hospitals, railway stations, bus terminals, airports, etc., and for movement of aged and physically challenged persons.
  27. Buildings which are having more than four storeys are provided with elevators or lifts. Lifts are operated hydraulically or by electric traction.
  28. Elevators are provided for different purposes and accordingly classified as Passenger lifts, Goods lifts, Hospital lifts, Service lifts and Fireman’s lifts.
  29. Escalators are the moving stairs which moves by using revolving drum. A few steps at top and bottom are kept level through moving individually.
  30. Different factors to be considered in the design of an escalator are: Speed and slope of escalator location.
REVIEW QUESTIONS
  1. Discuss the requirements of a good stair.
  2. List the components of a staircase.
  3. What are the various types of stairs used in buildings? Illustrate your answer with sketches.
  4. Draw a sectional elevation and plan of a dog-legged stair connecting two floors of a building.
  5. Enumerate and justify the essential requirements of a domestic staircase.
  6. Distinguish between quarter-turn and half-turn staircases used in buildings.
  7. What are the types of stone stairs? Illustrate with sketches.
  8. How are the stone stairs constructed and supported?
  9. Bing out the advantages of concrete stairs compared to other stairs.
  10. Explain the design principles of a staircase.

    11. (a) State briefly the requirements of a good staircase

    (b) How are treads and risers proportioned?

    (c) Where do you see:

    (i) Dog-legged stair

    (ii) Open-newel-stair, and

    (iii) Geometrical stair.(AMIE)

  11. A suitable stair has to be located in a staircase 7.67 m long, 4.54 m wide and 4.54 m high, with a door 1.22 m wide in each of the longitudinal walls. The doors face each other and are located with their centres at a distance of 1.07 m from the respective corners of the staircase. Assuming that it is in a public building, design the stair and draw a dimensional sketch plain and a dimensional sketch section to illustrate your proposals (AMIE)
  12. Indicate the situations where you would recommend (i) a ramp and (ii) an escalator.
  13. When it is necessary to provide elevators in a building? Give the components of a lift.
  14. What is an escalator? Discuss the essential requirements for its provision.
  15. Where do ramps are preferred?