Stair, lifts and escalators

Given data and assumptions

• Stairwell (internal): 4.6 m x 2.6 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.25$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.25 m side by side need $2b = 2.5$ m; the remaining $W - 2b = 2.6 - 2.5 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.25 m x 2.6 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.25 = 3.5$ m $\le 4.6$ m, so it fits; spare length 1.1 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.5 m, so depth $\approx$ span/20 $= 175$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.25 m.

Stairwell assumed as 4.5 m x 2.5 m (a normal size for a house).

Given data and assumptions

• Stairwell (internal): 4.5 m x 2.5 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.2$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.2 m side by side need $2b = 2.4$ m; the remaining $W - 2b = 2.5 - 2.4 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.2 m x 2.5 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.2 = 3.45$ m $\le 4.5$ m, so it fits; spare length 1.05 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.45 m, so depth $\approx$ span/20 $= 173$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.2 m.

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Essential elements of a stair

A stair has the following essential elements:

• Step: one riser plus one tread; steps are the basic unit.
• Tread and riser: tread is the horizontal surface (250-300 mm), riser the vertical face (150-175 mm).
• Nosing: the rounded projecting edge of the tread (about 25 mm).
• Flight: an unbroken series of steps between landings (3 to 12 steps).
• Landing: level platform at the ends of a flight or between flights; quarter-space or half-space.
• Going and rise: horizontal and vertical measurements of a step or flight.
• Waist slab / stringer: the inclined slab or beam which supports the steps.
• Soffit: underside of the flight.
• Handrail, baluster and newel post: the balustrade that protects the open sides; handrail about 0.9 m high.
• Headroom: clear height above the steps (min. about 2.0-2.2 m).
• Winder: tapered step used to turn the stair in restricted space.
• Pitch line: imaginary line joining the nosings; its angle with the horizontal is the pitch.

        handrail
          /|  baluster
   newel /_|__
        |    |  nosing
  riser |____|__ tread
  ______|
   going <--->

Types of stair (with sketches)

 Straight      Quarter turn     Dog-legged       Open well
 |  |  |       |  |_____       |>>>>>|           |>>>>>|
 |  |  |       |  |             |<<<<<|          |    |
 |  |  |       |__|             |_____|          |<<<<|
                                                  (well)
 Geometrical (spiral)           Bifurcated
     ___                           _|_
    / o \                         |   |
    \___/                          \ /

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Terminology used in stair construction

• Tread: the horizontal top surface of a step on which the foot is placed (usually 250-300 mm).
• Riser: the vertical face between two consecutive treads (usually 150-175 mm).
• Going: horizontal distance between the faces of two consecutive risers; total going is the horizontal length of the flight.
• Rise: vertical distance between two consecutive treads, or total vertical height of a flight.
• Nosing: the projecting edge of the tread beyond the riser (about 25 mm), usually rounded.
• Flight: an unbroken series of steps between two landings.
• Landing: a level platform between flights or at the start and end of a stair; a half-space landing turns the stair through 180 degrees, a quarter-space landing through 90 degrees.
• Winder: a tapered (radiating) step used to change direction.
• Soffit: the underside of a flight or landing.
• Waist: the thickness of the inclined RCC slab, measured perpendicular to the slope.
• Baluster: a vertical member (post) between the stair and the handrail.
• Balustrade: the complete protective barrier of balusters, handrail and newel posts.
• Handrail: the rail on top of the balusters, held by the hand (about 0.9 m high).
• Newel post: the main post at the start, end or turn of a flight which supports the handrail.
• Stringer: the inclined side beam that supports the steps.
• Headroom: the clear vertical distance from the pitch line (line joining nosings) to the soffit above (min. about 2.0-2.2 m).
• Pitch (slope): the angle between the pitch line and the horizontal, usually 25-40 degrees.
• Stair well (hoist way): the space in plan occupied by the stair.
• Scotia (apron): moulding under the nosing.

              handrail
          newel |   baluster
            ____|__|__|__
           |  .  .  .   /
    riser  |__/--------/ <- nosing
      tread  /  /  /  /   pitch line
       ____/ /  /  /
 going <---> soffit (underside)

A ladder is a set of rungs (steps) fixed between two side rails, set at a steep slope (60-90 degrees); it gives access to lofts, roofs, water tanks, manholes and for fire escape or maintenance. Fixed ladders are made of steel, timber or aluminium, with rungs 250-300 mm apart. It takes little space but is steep, unsafe for children and elderly, and not suitable for regular traffic.

   | |
   |=|  rung
   |=|
   |=|
   | |

A ramp is an inclined plane (without steps) connecting two floors at different levels; it carries wheelchairs, trolleys, bicycles, vehicles and stretchers.

• Slope: 1 in 12 for wheelchairs (maximum 1 in 10 for short lengths), 1 in 8 to 1 in 10 for goods and 1 in 6 to 1 in 8 for vehicles.
• Width at least 1.2 m (1.5 m in public buildings), with a level landing of at least 1.5 m x 1.5 m at the top, bottom and turns, and after every 9 m rise (as per NBC barrier-free requirements).
• Handrails at 0.8-0.9 m on both sides, kerb or edge protection, non-slip surface.
• Requires a long horizontal space: a rise of 1 m needs about 12 m of ramp.

        ______ upper level
       /|
      / | rise
 ____/__|
  length = 12 x rise

Terms

• Baluster: a vertical post (small column) that supports the handrail and fills the gap between handrail and steps.
• Nosing: the projecting rounded edge of the tread (about 25 mm) beyond the riser; it increases the foot space and gives a neat edge.
• Soffit: the underside (lower surface) of a flight or landing, usually plastered.
• Pitch: the angle of inclination of the stair, measured between the line joining the nosings (pitch line) and the horizontal; $\tan\theta = R/T$, usually 25-40 degrees.

        handrail
        |  baluster
        |  |
        |  |__ nosing
     ___|__|
  riser |  tread
  ___ __|
 pitch angle  soffit below

Types of stair

Two types explained

1. Dog-legged stair: two straight flights run in opposite directions, connected by a half-space landing; there is no well between the flights, so they look like a dog's leg. It takes little floor area and is very common in houses and public buildings.

 +----------+-------+
 | <<< DN   |       |
 +----------+  L    |
 | >>> UP   |       |
 +----------+-------+

2. Quarter-turn stair: the direction of the stair changes by 90 degrees at a quarter-space landing (square landing); it is used where the stair turns at a corner of a hall.

 +-----+
 | F2  |
 | ^   |
 +-----+------------+
 | L   | F1 >>>>>   |
 +-----+------------+

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Elements of a staircase

A stair has the following essential elements:

• Step: one riser plus one tread; steps are the basic unit.
• Tread and riser: tread is the horizontal surface (250-300 mm), riser the vertical face (150-175 mm).
• Nosing: the rounded projecting edge of the tread (about 25 mm).
• Flight: an unbroken series of steps between landings (3 to 12 steps).
• Landing: level platform at the ends of a flight or between flights; quarter-space or half-space.
• Going and rise: horizontal and vertical measurements of a step or flight.
• Waist slab / stringer: the inclined slab or beam which supports the steps.
• Soffit: underside of the flight.
• Handrail, baluster and newel post: the balustrade that protects the open sides; handrail about 0.9 m high.
• Headroom: clear height above the steps (min. about 2.0-2.2 m).
• Winder: tapered step used to turn the stair in restricted space.
• Pitch line: imaginary line joining the nosings; its angle with the horizontal is the pitch.

        handrail
          /|  baluster
   newel /_|__
        |    |  nosing
  riser |____|__ tread
  ______|
   going <--->

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Essential requirements of a good stair

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Types of stair as per shape

Essential elements of a stair

A stair has the following essential elements:

• Step: one riser plus one tread; steps are the basic unit.
• Tread and riser: tread is the horizontal surface (250-300 mm), riser the vertical face (150-175 mm).
• Nosing: the rounded projecting edge of the tread (about 25 mm).
• Flight: an unbroken series of steps between landings (3 to 12 steps).
• Landing: level platform at the ends of a flight or between flights; quarter-space or half-space.
• Going and rise: horizontal and vertical measurements of a step or flight.
• Waist slab / stringer: the inclined slab or beam which supports the steps.
• Soffit: underside of the flight.
• Handrail, baluster and newel post: the balustrade that protects the open sides; handrail about 0.9 m high.
• Headroom: clear height above the steps (min. about 2.0-2.2 m).
• Winder: tapered step used to turn the stair in restricted space.
• Pitch line: imaginary line joining the nosings; its angle with the horizontal is the pitch.

        handrail
          /|  baluster
   newel /_|__
        |    |  nosing
  riser |____|__ tread
  ______|
   going <--->

Ladder

A ladder is a set of rungs (steps) fixed between two side rails, set at a steep slope (60-90 degrees); it gives access to lofts, roofs, water tanks, manholes and for fire escape or maintenance. Fixed ladders are made of steel, timber or aluminium, with rungs 250-300 mm apart. It takes little space but is steep, unsafe for children and elderly, and not suitable for regular traffic.

   | |
   |=|  rung
   |=|
   |=|
   | |

Lift and elevator

A lift (elevator) is a mechanical device which carries persons or goods between floors in a vertical shaft by a car moving on guide rails. Main parts: lift car, hoist way (shaft), guide rails, counterweight, wire ropes, traction machine and motor in the machine room (or machine-room-less), control panel, safety gear and buffers, landing doors and a pit.

• Types by drive: electric traction, hydraulic and machine-room-less (MRL) lifts.
• Types by use: passenger, goods (freight), hospital (bed), service and observation lifts.
• Speed 0.5-1 m/s for low-rise, 1.5-2.5 m/s for high-rise buildings. Provided in every building with more than about 4-5 storeys (as per NBC) and fire lifts in tall buildings.

  machine room
   [motor]
     |   |
   [CW] [CAR]
     |   |
     |   |   <- guide rails
   ---pit---

An elevator is the American term for a lift; both mean the same.

Ramp

A ramp is an inclined plane (without steps) connecting two floors at different levels; it carries wheelchairs, trolleys, bicycles, vehicles and stretchers.

• Slope: 1 in 12 for wheelchairs (maximum 1 in 10 for short lengths), 1 in 8 to 1 in 10 for goods and 1 in 6 to 1 in 8 for vehicles.
• Width at least 1.2 m (1.5 m in public buildings), with a level landing of at least 1.5 m x 1.5 m at the top, bottom and turns, and after every 9 m rise (as per NBC barrier-free requirements).
• Handrails at 0.8-0.9 m on both sides, kerb or edge protection, non-slip surface.
• Requires a long horizontal space: a rise of 1 m needs about 12 m of ramp.

        ______ upper level
       /|
      / | rise
 ____/__|
  length = 12 x rise

Two methods that suit wheelchair users:

1. Ramp

A ramp is an inclined plane (without steps) connecting two floors at different levels; it carries wheelchairs, trolleys, bicycles, vehicles and stretchers.

• Slope: 1 in 12 for wheelchairs (maximum 1 in 10 for short lengths), 1 in 8 to 1 in 10 for goods and 1 in 6 to 1 in 8 for vehicles.
• Width at least 1.2 m (1.5 m in public buildings), with a level landing of at least 1.5 m x 1.5 m at the top, bottom and turns, and after every 9 m rise (as per NBC barrier-free requirements).
• Handrails at 0.8-0.9 m on both sides, kerb or edge protection, non-slip surface.
• Requires a long horizontal space: a rise of 1 m needs about 12 m of ramp.

        ______ upper level
       /|
      / | rise
 ____/__|
  length = 12 x rise

2. Lift (elevator)

A lift with a car of at least 1.1 m x 1.4 m (clear door width 0.9 m), control buttons at 0.9-1.2 m height with Braille markings, handrail in the car, voice announcement and levelling accuracy of 10-12 mm at every floor. It is the best choice for high-rise buildings.

Another aid is the platform (stair) lift, a small motorised platform that moves along a stair and is used where a ramp cannot fit.

Lifts

A lift (elevator) is a mechanical device which carries persons or goods between floors in a vertical shaft by a car moving on guide rails. Main parts: lift car, hoist way (shaft), guide rails, counterweight, wire ropes, traction machine and motor in the machine room (or machine-room-less), control panel, safety gear and buffers, landing doors and a pit.

Escalators

An escalator is a moving stair: a continuous chain of steps driven by an electric motor, which carries a large number of people between floors at 0.5-0.65 m/s.

• Inclination 30 degrees (35 degrees max), step width 600, 800 or 1000 mm, capacity 4000-9000 persons/hour.
• Parts: truss, steps, step chain, handrail, comb plate, drive motor, balustrade and safety switches.
• Used in shopping malls, airports, railway stations and metro stations where heavy traffic moves continuously. It occupies more floor area than a lift and needs an emergency stair in addition.

Passenger lift

Carries people; car size and capacity depend on use (6, 8, 13, 20 persons; e.g. a 6-person car is about 1.1 m x 1.4 m). Speed 1-2.5 m/s, smooth acceleration, decorated cabin, ventilation, alarm, emergency light and automatic doors. Located near the main entrance, lobby space in front, and designed to NBC for number of lifts per floor area.

Freight (goods) lift

Carries goods and loads up to 500-5000 kg or more; larger and stronger car with strong floor, usually slow (0.25-0.5 m/s), simple finish, wide doors (vertical sliding or double leaf), operated by trained staff; used in warehouses, factories and hotels.

Elevator and ramp

An elevator (lift) is a mechanical device which carries persons or goods vertically between floors in a shaft, using a car, guide rails, ropes and a counterweight. A ramp is a sloping surface, without steps, joining two levels (slope 1 in 12 for wheelchairs).

Design of dog-legged stair

Stairwell assumed as 4.5 m x 2.5 m.

Given data and assumptions

• Stairwell (internal): 4.5 m x 2.5 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.2$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.2 m side by side need $2b = 2.4$ m; the remaining $W - 2b = 2.5 - 2.4 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.2 m x 2.5 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.2 = 3.45$ m $\le 4.5$ m, so it fits; spare length 1.05 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.45 m, so depth $\approx$ span/20 $= 173$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.2 m.

Escalator

An escalator is a moving stair: a continuous chain of steps driven by an electric motor, which carries a large number of people between floors at 0.5-0.65 m/s.

• Inclination 30 degrees (35 degrees max), step width 600, 800 or 1000 mm, capacity 4000-9000 persons/hour.
• Parts: truss, steps, step chain, handrail, comb plate, drive motor, balustrade and safety switches.
• Used in shopping malls, airports, railway stations and metro stations where heavy traffic moves continuously. It occupies more floor area than a lift and needs an emergency stair in addition.

Design of staircase for municipal office

Given data and assumptions

• Stairwell (internal): 4.9 m x 2.7 m; floor-to-floor height $H = 3$ m; stair for a municipal office (public) building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.3$ m. A tread of 300 mm and riser of 150 mm are taken for a public building.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.3 = 2.7$ m.
4. Width: two flights of 1.3 m side by side need $2b = 2.6$ m; the remaining $W - 2b = 2.7 - 2.6 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.3 m x 2.7 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.7 + 1.3 = 4$ m $\le 4.9$ m, so it fits; spare length 0.9 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 300 = 600$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.6^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4 m, so depth $\approx$ span/20 $= 200$ mm; adopt 200 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 300 mm; 2 flights x 10 risers; flight width 1.3 m.

Given data and assumptions

• Stairwell (internal): 5 m x 2.1 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 167$ mm and tread $T = 240$ mm; flight width $b = 0.9$ m. A narrow well of 2.1 m width limits the cross flight, so a riser of about 167 mm and tread of 240 mm are taken (maximum riser for dwellings is 175 mm).

Design

1. Number of risers $= H/R = 3/0.167 = 18$, adopt 18 risers; exact riser $= 3/18 = 166.7$ mm.
2. Flights: a quarter-turn stair has a square quarter landing. Take flight 1 = 12 risers (11 treads) and flight 2 = 6 risers (5 treads); total 12+6 = 18 risers.
3. Goings: flight 1 $= 11 \times 0.24 = 2.64$ m; flight 2 $= 5 \times 0.24 = 1.2$ m.
4. Quarter landing: 0.9 m x 0.9 m at height $= 12 \times 0.167 = 2$ m.
5. Fit along the length: $2.64 + 0.9 = 3.54$ m $\le 5$ m.
6. Fit along the width: $0.9 + 1.2 = 2.1$ m $\le 2.1$ m.
7. Check: $2R + T = 2 \times 166.7 + 240 = 573$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 34.8^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.54 m, so depth $\approx$ span/20 $= 177$ mm; adopt 200 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +----+--------------------+
 | F2 |                    |
 | ^  |                    |
 | ^  |      (hall)        |
 +----+--------------------+
 |LAND| F1  >>>>>>>>>>>>   |
 +----+--------------------+
 F1 = 12 risers, quarter landing, F2 = 6 risers

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 18 risers of 166.7 mm and treads of 240 mm; flights of 12 and 6 risers; flight width 0.9 m.

Data: lobby 6.0 m x 4.2 m, floor height 4.5 m, slab thickness 150 mm, riser 150 mm, steps per flight not more than 12.

Given data and assumptions

• Stairwell (internal): 6 m x 4.2 m; floor-to-floor height $H = 4.5$ m; stair for a public building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.4$ m. Since 30 risers cannot be put in one flight of 12, a three-flight (zig-zag) stair with two landings is adopted.

Design

1. Number of risers $= H/R = 4.5/0.15 = 30$, adopt 30 risers; exact riser $= 4.5/30 = 150$ mm.
2. Flights: at most 12 risers per flight are allowed, so 30 risers are divided into three equal flights of 10 risers (9 treads each), arranged side by side in a zig-zag with two half-space landings (one at each end).
3. Going of one flight $= 9 \times 0.3 = 2.7$ m.
4. Width: three bays of 1.4 m give $3b = 4.2$ m $\le 4.2$ m.
5. Landings: two landings, each 1.4 m x 2.8 m, at heights 1.5 m and 3 m.
6. Length check: $2.7 + 1.4 = 4.1$ m $\le 6$ m.
7. Check: $2R + T = 2 \times 150 + 300 = 600$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.6^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.1 m, so depth $\approx$ span/20 $= 205$ mm; adopt 225 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 far end
 +---------+---------+---------+
 |  LANDING L1       |   F3    |
 +---------+---------+   ^     |
 |   F1    |   F2    |   ^     |
 |   ^     |   v     |   ^     |
 +---------+---------+   ^     |
 |  start  | LANDING L2        |
 +---------+---------+---------+
 near end   (F1 up, F2 down, F3 up)

 SECTION (not to scale)
                          +---- upper floor 4.5 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 30 risers of 150 mm and treads of 300 mm; 3 flights x 10 risers; flight width 1.4 m.

Floor-to-floor height $= 3.4 + 0.15 = 3.55$ m (clear height plus slab). Stair room 6.5 m (length) x 5.5 m (width). The width is large, so a U-shaped open-well stair with two flights of 1.8 m width is adopted.

Given data and assumptions

• Stairwell (internal): 6.5 m x 5.5 m; floor-to-floor height $H = 3.55$ m; stair for a public building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.8$ m.

Design

1. Number of risers $= H/R = 3.55/0.15 = 23.67$, adopt 24 risers; exact riser $= 3.55/24 = 147.9$ mm.
2. Flights: open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 12 risers and 11 treads.
3. Going of one flight $= 11 \times 0.3 = 3.3$ m.
4. Open well: $W - 2b = 5.5 - 3.6 = 1.9$ m wide open well is left between the flights and protected by a balustrade.
5. Landing: 1.8 m x 5.5 m at height $= 12 \times 0.148 = 1.77$ m.
6. Length check: $3.3 + 1.8 = 5.1$ m $\le 6.5$ m, so it fits.
7. Check: $2R + T = 2 \times 147.9 + 300 = 596$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.2^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 5.1 m, so depth $\approx$ span/20 $= 255$ mm; adopt 275 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<       |         |
 |                        | LANDING |
 +- - - open well - - - - +         |
 | FLIGHT 1  >>>>>>  UP   |         |
 +------------------------+---------+

 SECTION (not to scale)
                          +---- upper floor 3.55 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 24 risers of 147.9 mm and treads of 300 mm; 2 flights x 12 risers; flight width 1.8 m.

Hospital stairs need a wide flight for stretchers and a low riser (not more than 150 mm). The height 4.2 m with not more than 12 steps per flight gives three flights.

Given data and assumptions

• Stairwell (internal): 6 m x 4.5 m; floor-to-floor height $H = 4.2$ m; stair for a hospital building, RCC.
• Assumed riser $R = 140$ mm and tread $T = 300$ mm; flight width $b = 1.5$ m. Riser reduced to 140 mm for patients and elderly persons.

Design

1. Number of risers $= H/R = 4.2/0.14 = 30$, adopt 30 risers; exact riser $= 4.2/30 = 140$ mm.
2. Flights: at most 12 risers per flight are allowed, so 30 risers are divided into three equal flights of 10 risers (9 treads each), arranged side by side in a zig-zag with two half-space landings (one at each end).
3. Going of one flight $= 9 \times 0.3 = 2.7$ m.
4. Width: three bays of 1.5 m give $3b = 4.5$ m $\le 4.5$ m.
5. Landings: two landings, each 1.5 m x 3 m, at heights 1.4 m and 2.8 m.
6. Length check: $2.7 + 1.5 = 4.2$ m $\le 6$ m.
7. Check: $2R + T = 2 \times 140 + 300 = 580$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 25^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.2 m, so depth $\approx$ span/20 $= 210$ mm; adopt 225 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 far end
 +---------+---------+---------+
 |  LANDING L1       |   F3    |
 +---------+---------+   ^     |
 |   F1    |   F2    |   ^     |
 |   ^     |   v     |   ^     |
 +---------+---------+   ^     |
 |  start  | LANDING L2        |
 +---------+---------+---------+
 near end   (F1 up, F2 down, F3 up)

 SECTION (not to scale)
                          +---- upper floor 4.2 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 30 risers of 140 mm and treads of 300 mm; 3 flights x 10 risers; flight width 1.5 m.

Stair

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Design of quarter turn stair

Assumed: riser 150 mm, tread 250 mm, flight width 1.1 m, lobby 5.5 m x 4.0 m.

Given data and assumptions

• Stairwell (internal): 5.5 m x 4 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.1$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a quarter-turn stair has a square quarter landing. Take flight 1 = 12 risers (11 treads) and flight 2 = 8 risers (7 treads); total 12+8 = 20 risers.
3. Goings: flight 1 $= 11 \times 0.25 = 2.75$ m; flight 2 $= 7 \times 0.25 = 1.75$ m.
4. Quarter landing: 1.1 m x 1.1 m at height $= 12 \times 0.15 = 1.8$ m.
5. Fit along the length: $2.75 + 1.1 = 3.85$ m $\le 5.5$ m.
6. Fit along the width: $1.1 + 1.75 = 2.85$ m $\le 4$ m.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.85 m, so depth $\approx$ span/20 $= 192$ mm; adopt 200 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +----+--------------------+
 | F2 |                    |
 | ^  |                    |
 | ^  |      (hall)        |
 +----+--------------------+
 |LAND| F1  >>>>>>>>>>>>   |
 +----+--------------------+
 F1 = 12 risers, quarter landing, F2 = 8 risers

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; flights of 12 and 8 risers; flight width 1.1 m.

Floor-to-floor height $= 3.5 + 0.15 = 3.65$ m (clear distance plus slab). Hall 7.5 m (length) x 5.5 m (width). A wide U-shaped open-well stair is adopted with 1.8 m wide flights.

Given data and assumptions

• Stairwell (internal): 7.5 m x 5.5 m; floor-to-floor height $H = 3.65$ m; stair for a public building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.8$ m.

Design

1. Number of risers $= H/R = 3.65/0.15 = 24.33$, adopt 24 risers; exact riser $= 3.65/24 = 152.1$ mm.
2. Flights: open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 12 risers and 11 treads.
3. Going of one flight $= 11 \times 0.3 = 3.3$ m.
4. Open well: $W - 2b = 5.5 - 3.6 = 1.9$ m wide open well is left between the flights and protected by a balustrade.
5. Landing: 1.8 m x 5.5 m at height $= 12 \times 0.152 = 1.82$ m.
6. Length check: $3.3 + 1.8 = 5.1$ m $\le 7.5$ m, so it fits.
7. Check: $2R + T = 2 \times 152.1 + 300 = 604$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.9^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 5.1 m, so depth $\approx$ span/20 $= 255$ mm; adopt 275 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<       |         |
 |                        | LANDING |
 +- - - open well - - - - +         |
 | FLIGHT 1  >>>>>>  UP   |         |
 +------------------------+---------+

 SECTION (not to scale)
                          +---- upper floor 3.65 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 24 risers of 152.1 mm and treads of 300 mm; 2 flights x 12 risers; flight width 1.8 m.

Data: stair room 3.9 m x 1.8 m, floor height 2.4 m, waist slab thickness 150 mm. A straight flight with a tread of 260 mm is adopted to use the 3.9 m length fully.

Given data and assumptions

• Stairwell (internal): 3.9 m x 1.8 m; floor-to-floor height $H = 2.4$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 260$ mm; flight width $b = 1.8$ m.

Design

1. Number of risers $= H/R = 2.4/0.15 = 16$, adopt 16 risers; exact riser $= 2.4/16 = 150$ mm.
2. Treads $= 16-1 = 15$; going of the flight $= 15 \times 0.26 = 3.9$ m $\le 3.9$ m, so a single straight flight fits.
3. Width: flight width 1.8 m $\le 1.8$ m (a middle handrail can be added since the flight is wide).
4. Check: $2R + T = 2 \times 150 + 260 = 560$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 30^\circ$ (within 25-40 degrees).
5. Waist slab: effective span about 5.7 m, so depth $\approx$ span/20 $= 285$ mm; adopt 150 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +-----------------------------------+
 |  >>>>>> straight flight (UP) >>>> |
 +-----------------------------------+

 SECTION (not to scale)
                          +---- upper floor 2.4 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 16 risers of 150 mm and treads of 260 mm; 1 flight x 16 risers; flight width 1.8 m.

Given data and assumptions

• Stairwell (internal): 4.5 m x 2.1 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1 m side by side need $2b = 2$ m; the remaining $W - 2b = 2.1 - 2 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1 m x 2.1 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1 = 3.25$ m $\le 4.5$ m, so it fits; spare length 1.25 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.25 m, so depth $\approx$ span/20 $= 162$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1 m.

Flight width $b = 1.2$ m. Stairwell width $= 2 \times 1.2 + 0.1 = 2.5$ m and length assumed 4.5 m.

Given data and assumptions

• Stairwell (internal): 4.5 m x 2.5 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.2$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.2 m side by side need $2b = 2.4$ m; the remaining $W - 2b = 2.5 - 2.4 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.2 m x 2.5 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.2 = 3.45$ m $\le 4.5$ m, so it fits; spare length 1.05 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.45 m, so depth $\approx$ span/20 $= 173$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.2 m.

Elements for vertical circulation

1. Stair: the most common, with flights and landings.
2. Ramp: sloping surface (1:12) for wheelchairs and trolleys.
3. Lift (elevator): mechanical car in a shaft for persons or goods.
4. Escalator: moving stair for heavy traffic.
5. Ladder: steep rung access to lofts and roof.
6. Paternoster, chute and fire escape: other special devices.

Design of RCC dog-legged stair

Room 4.5 m x 2.3 m, floor height 3.0 m.

Given data and assumptions

• Stairwell (internal): 4.5 m x 2.3 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.1$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.1 m side by side need $2b = 2.2$ m; the remaining $W - 2b = 2.3 - 2.2 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.1 m x 2.3 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.1 = 3.35$ m $\le 4.5$ m, so it fits; spare length 1.15 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.35 m, so depth $\approx$ span/20 $= 168$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.1 m.

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Given data and assumptions

• Stairwell (internal): 4.8 m x 2.25 m; floor-to-floor height $H = 3.6$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 280$ mm; flight width $b = 1.05$ m. Gap between the flights = 2.25 - 2 x 1.05 = 0.15 m.

Design

1. Number of risers $= H/R = 3.6/0.15 = 24$, adopt 24 risers; exact riser $= 3.6/24 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 24/2 = 12 risers and 12-1 = 11 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 11 \times 0.28 = 3.08$ m.
4. Width: two flights of 1.05 m side by side need $2b = 2.1$ m; the remaining $W - 2b = 2.25 - 2.1 = 0.15$ m is the well gap between the flights.
5. Landing: a half-space landing 1.05 m x 2.25 m (full stairwell width) at height $= 12 \times 0.15 = 1.8$ m.
6. Length check: going + landing $= 3.08 + 1.05 = 4.13$ m $\le 4.8$ m, so it fits; spare length 0.67 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 280 = 580$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 28.2^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.13 m, so depth $\approx$ span/20 $= 206$ mm; adopt 225 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 11 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 11 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3.6 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 24 risers of 150 mm and treads of 280 mm; 2 flights x 12 risers; flight width 1.05 m.

Reasons for the size of riser and tread

• Riser 150 mm: an office building has heavy traffic of all ages, so the riser is kept at the lower limit (150 mm) for comfortable climbing; floor height 3.6 m divides exactly into 24 equal risers.
• Tread 280 mm: a wide tread (250-300 mm) gives safe foot placing; $2R + T = 2 \times 150 + 280 = 580$ mm, which is within the usual comfort range of 550-650 mm.
• Equal riser and tread throughout so that people do not trip.

Given data and assumptions

• Stairwell (internal): 4.8 m x 3 m; floor-to-floor height $H = 3.6$ m; stair for a office building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 280$ mm; flight width $b = 1.45$ m. Stair size 4.8 m x 3.0 m x 3.6 m (length x width x height). Gap between flights = 3.0 - 2 x 1.45 = 0.1 m.

Design

1. Number of risers $= H/R = 3.6/0.15 = 24$, adopt 24 risers; exact riser $= 3.6/24 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 24/2 = 12 risers and 12-1 = 11 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 11 \times 0.28 = 3.08$ m.
4. Width: two flights of 1.45 m side by side need $2b = 2.9$ m; the remaining $W - 2b = 3 - 2.9 = 0.1$ m is the well gap between the flights.
5. Landing: a half-space landing 1.45 m x 3 m (full stairwell width) at height $= 12 \times 0.15 = 1.8$ m.
6. Length check: going + landing $= 3.08 + 1.45 = 4.53$ m $\le 4.8$ m, so it fits; spare length 0.27 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 280 = 580$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 28.2^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.53 m, so depth $\approx$ span/20 $= 226$ mm; adopt 250 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 11 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 11 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3.6 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 24 risers of 150 mm and treads of 280 mm; 2 flights x 12 risers; flight width 1.45 m.

Details to be drawn

• Plan at ground floor and first floor with arrows UP/DN, flight width and landing.
• Section showing 150 mm riser, 280 mm tread, waist slab, landing slab, nosing (25 mm) and balustrade (0.9 m high).
• Reinforcement: main bars along the slope (e.g. 12 mm dia at 150 c/c), distribution bars 8 mm at 200 c/c, concrete M20, steel Fe415 (to be designed separately).

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Functional requirements of a good stair

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Given data and assumptions

• Stairwell (internal): 5 m x 4 m; floor-to-floor height $H = 3$ m; stair for a public building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.9$ m. Wide flights of 1.9 m (public building) leave a gap of 4.0 - 2 x 1.9 = 0.2 m between the flights.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.3 = 2.7$ m.
4. Width: two flights of 1.9 m side by side need $2b = 3.8$ m; the remaining $W - 2b = 4 - 3.8 = 0.2$ m is the well gap between the flights.
5. Landing: a half-space landing 1.9 m x 4 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.7 + 1.9 = 4.6$ m $\le 5$ m, so it fits; spare length 0.4 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 300 = 600$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.6^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.6 m, so depth $\approx$ span/20 $= 230$ mm; adopt 250 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 300 mm; 2 flights x 10 risers; flight width 1.9 m.

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Ideal requirements of a stair

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Types of stair by shape in plan

 Straight   Quarter turn   Dog-legged   Open well   Spiral
 | |        |__             |>>|<<|      |>>|  |     ( o )
 | |        |  |_           |__|__|      |__|<<|
 | |        |__|

Design of open-well staircase

Floor-to-floor height $= 3.0 + 0.12 = 3.12$ m (ceiling height plus slab thickness). Hall 6.0 m x 3.5 m. Riser about 156 mm so that 20 equal risers are obtained.

Given data and assumptions

• Stairwell (internal): 6 m x 3.5 m; floor-to-floor height $H = 3.12$ m; stair for a public building, RCC.
• Assumed riser $R = 156$ mm and tread $T = 300$ mm; flight width $b = 1.5$ m.

Design

1. Number of risers $= H/R = 3.12/0.156 = 20$, adopt 20 risers; exact riser $= 3.12/20 = 156$ mm.
2. Flights: open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 10 risers and 9 treads.
3. Going of one flight $= 9 \times 0.3 = 2.7$ m.
4. Open well: $W - 2b = 3.5 - 3 = 0.5$ m wide open well is left between the flights and protected by a balustrade.
5. Landing: 1.5 m x 3.5 m at height $= 10 \times 0.156 = 1.56$ m.
6. Length check: $2.7 + 1.5 = 4.2$ m $\le 6$ m, so it fits.
7. Check: $2R + T = 2 \times 156 + 300 = 612$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 27.5^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.2 m, so depth $\approx$ span/20 $= 210$ mm; adopt 225 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<       |         |
 |                        | LANDING |
 +- - - open well - - - - +         |
 | FLIGHT 1  >>>>>>  UP   |         |
 +------------------------+---------+

 SECTION (not to scale)
                          +---- upper floor 3.12 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 156 mm and treads of 300 mm; 2 flights x 10 risers; flight width 1.5 m.

A stair is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade.

Ideal requirements of a stair

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Types of stair by shape

 Straight   Quarter turn   Dog-legged   Open well   Spiral
 | |        |__             |>>|<<|      |>>|  |     ( o )
 | |        |  |_           |__|__|      |__|<<|
 | |        |__|

Design of dog-legged stair

Lobby 4.5 m x 3.0 m, floor height 3.0 m, residential. Flight width 1.2 m, so the gap between flights is 3.0 - 2 x 1.2 = 0.6 m.

Given data and assumptions

• Stairwell (internal): 4.5 m x 3 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.2$ m.

Design

1. Number of risers $= H/R = 3/0.15 = 20$, adopt 20 risers; exact riser $= 3/20 = 150$ mm.
2. Flights: a dog-legged stair has two equal flights, so each flight has 20/2 = 10 risers and 10-1 = 9 treads (the upper floor itself acts as the last tread).
3. Going of one flight $= 9 \times 0.25 = 2.25$ m.
4. Width: two flights of 1.2 m side by side need $2b = 2.4$ m; the remaining $W - 2b = 3 - 2.4 = 0.6$ m is the well gap between the flights.
5. Landing: a half-space landing 1.2 m x 3 m (full stairwell width) at height $= 10 \times 0.15 = 1.5$ m.
6. Length check: going + landing $= 2.25 + 1.2 = 3.45$ m $\le 4.5$ m, so it fits; spare length 1.05 m is kept as entry/exit space.
7. Check: $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 3.45 m, so depth $\approx$ span/20 $= 173$ mm; adopt 175 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  DN   |         |
 | 9 treads             | LANDING |
 +------------------------+  (b x   |
 | FLIGHT 1  >>>>>>  UP   |   2b+g) |
 | 9 treads             |         |
 +------------------------+---------+
 <------ going ---------> <-- b -->
 (entry at left end of flight 1)

 SECTION (not to scale)
                          +---- upper floor 3 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 20 risers of 150 mm and treads of 250 mm; 2 flights x 10 risers; flight width 1.2 m.

Functional requirements of a good staircase

1. Location: easily accessible, centrally placed, well lit and ventilated, and near the main entrance; not through rooms.
2. Width: residential at least 0.9-1.0 m, public buildings 1.5 m or more (as per NBC and local building bye-laws), so that two persons can pass.
3. Easy and safe ascent: riser 150-175 mm (public buildings not more than 150 mm), tread 250-300 mm; $2R + T$ about 580-600 mm; all steps in one flight equal.
4. Pitch: between 25 and 40 degrees.
5. Number of steps per flight: not more than 12 and not less than 3 steps.
6. Landings: provided at turns and between flights, width not less than the stair width.
7. Headroom: at least 2.0-2.2 m clear above every step.
8. Strength and fire resistance: strong enough for live load; material fire resistant, with a separate fire-escape stair in tall buildings.
9. Handrails and balustrades: about 0.9 m high, strong and safe for children.
10. Surface: non-slip treads, good lighting and ventilation, durable and pleasing in appearance.

Types of staircase by shape

 Straight   Quarter turn   Dog-legged   Open well   Spiral
 | |        |__             |>>|<<|      |>>|  |     ( o )
 | |        |  |_           |__|__|      |__|<<|
 | |        |__|

Design of open-well staircase

Room 5.5 m x 3.5 m, floor height 3.6 m, public building.

Given data and assumptions

• Stairwell (internal): 5.5 m x 3.5 m; floor-to-floor height $H = 3.6$ m; stair for a public building, RCC.
• Assumed riser $R = 150$ mm and tread $T = 300$ mm; flight width $b = 1.5$ m.

Design

1. Number of risers $= H/R = 3.6/0.15 = 24$, adopt 24 risers; exact riser $= 3.6/24 = 150$ mm.
2. Flights: open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 12 risers and 11 treads.
3. Going of one flight $= 11 \times 0.3 = 3.3$ m.
4. Open well: $W - 2b = 3.5 - 3 = 0.5$ m wide open well is left between the flights and protected by a balustrade.
5. Landing: 1.5 m x 3.5 m at height $= 12 \times 0.15 = 1.8$ m.
6. Length check: $3.3 + 1.5 = 4.8$ m $\le 5.5$ m, so it fits.
7. Check: $2R + T = 2 \times 150 + 300 = 600$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 26.6^\circ$ (within 25-40 degrees).
8. Waist slab: effective span about 4.8 m, so depth $\approx$ span/20 $= 240$ mm; adopt 250 mm thick waist slab (reinforcement to be designed separately). Provide handrail 0.9 m high, 20-25 mm nosing and non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<       |         |
 |                        | LANDING |
 +- - - open well - - - - +         |
 | FLIGHT 1  >>>>>>  UP   |         |
 +------------------------+---------+

 SECTION (not to scale)
                          +---- upper floor 3.6 m
                    _____|
               ____|   flight 2
        ______|  landing
   ____|  flight 1
 _|
 ground floor +0.00

Summary

Answer: 24 risers of 150 mm and treads of 300 mm; 2 flights x 12 risers; flight width 1.5 m.