--- title: "Stair for hospital (6.0 m ร— 4.5 m lobby)" subject: "Building Technology" chapter: 5 key: "semester_6/building_technology:stair-hospital" source: https://www.bctengineer.com/q/semester_6/building_technology/stair-hospital site: BCT Engineering --- # Stair for hospital (6.0 m ร— 4.5 m lobby) Building Technology ยท Chapter 5: Stair, lifts and escalators - Asked in: 2076 Bhadra, 6 marks - Video: [๐Ÿšจ Exit Staircase Requirements | NBC I Design & Safety Norms Explained ๐Ÿšจ](https://www.youtube.com/watch?v=hcfGhp7Yguk) โ€” Fire Safe India by MK - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/stair-hospital - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-5 ## Question Design and draw plan of a stair for a hospital building in a lobby of size 6.0m * 4.5m. The floor to floor height is 4.2m, where you cannot keep more than 12 steps in one flight. ## Short answer Three-flight zig-zag stair with 30 risers of 140 mm, treads 300 mm, three flights of 10 risers each, flight width 1.5 m. ## Answer Hospital stairs need a wide flight for stretchers and a low riser (not more than 150 mm). A height of 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. The riser is 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 the 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 (covering two bays), at heights 1.4 m and 2.8 m. 6. **Length check:** landing L1 + going + landing L2 $= 1.5 + 2.7 + 1.5 = 5.7$ m $\le 6$ m, so it fits; the spare 0.3 m is kept at the entry. 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 (going + one landing), so depth $\approx$ span/20 $= 210$ mm; adopt a 225 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 ```text far end +-------------------+---------+ | LANDING L1 | arrival | | (+1.40 m) | (upper | | | floor) | +---------+---------+---------+ | F1 | F2 | F3 | | ^ | v | ^ | | ^ | v | ^ | +---------+---------+---------+ | start | LANDING L2 | | | (+2.80 m) | +---------+-------------------+ near end (arrows point up the stair) ``` ```text SECTION (not to scale) +---- upper floor +4.20 _____| flight 3 _____| landing L2 +2.80 _____| flight 2 _____| landing L1 +1.40 ____| flight 1 ___| ground floor +0.00 ``` #### Summary | Item | Adopted | |---|---| | Riser | 140 mm (30 nos.) | | Tread | 300 mm | | Flights | 3 flights x 10 risers | | Width of flight | 1.5 m | | Waist slab | 225 mm | **Answer: 30 risers of 140 mm and treads of 300 mm; 3 flights x 10 risers; flight width 1.5 m.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is the riser reduced to 140 mm? A. For patients and elderly persons B. To reduce cost C. To shorten the lobby D. To lower the slab Answer: A. Low risers ease climbing for patients and elderly. (Key point: Riser) 2. H = 4.2 m, R = 140 mm gives 30 risers. With max 12 per flight, what is adopted? A. Two flights of 15 B. Three flights of 10 C. Five flights of 6 D. One flight Answer: B. Three flights of 10 risers, zig-zag with two landings. (Key point: Flights) 3. Three bays of 1.5 m need A. 3.0 m B. 4.5 m C. 6.0 m D. 1.5 m Answer: B. 3 x 1.5 = 4.5 m, equal to the lobby width. (Key point: Width) 4. Landings of the hospital stair lie at A. 1.4 m and 2.8 m B. 1.5 m and 3 m C. 2.1 m only D. 4.2 m Answer: A. 10 x 0.14 = 1.4 m and 20 x 0.14 = 2.8 m. 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