Staircase for municipal office (4900 × 2700 mm)

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 about 4500-9000 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 an emergency stair is still needed 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 a riser of 150 mm are taken because this is 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 landing or upper floor 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 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; the spare 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 a 200 mm thick waist slab (reinforcement to be designed separately). Provide a handrail 0.9 m high, 20-25 mm nosing and a non-slip finish.

Plan and section

 +------------------------+---------+
 | FLIGHT 2  <<<<<<  UP   |         |
 | 9 treads               | LANDING |
 +------------------------+ (b x W) |
 | FLIGHT 1  >>>>>>  UP   |         |
 | 9 treads               |         |
 +------------------------+---------+
 <-------- going -------> <-- b -->
 (entry at left end of flight 1; arrows point up the stair)

 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.