--- title: "Open-well staircase (6.0 m × 3.5 m hall)" subject: "Building Technology" chapter: 5 key: "semester_6/building_technology:stair-064j" source: https://www.bctengineer.com/q/semester_6/building_technology/stair-064j site: BCT Engineering --- # Open-well staircase (6.0 m × 3.5 m hall) Building Technology · Chapter 5: Stair, lifts and escalators - Asked in: 2064 Jestha (old course), 16 marks - Video: [Staircase Part: 1 Design criteria and guidelines](https://www.youtube.com/watch?v=ZE0Jt_E_seQ) — My Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/stair-064j - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-5 ## Question Define staircase. Illustrate ideal requirements of the stair. Describe the different types of stair by shape in plan with neat sketches. Design an open-well staircase for a public building in a hall of 6.0m × 3.5m and ceiling height 3.0m. The thickness of the floor slab is 120mm. Assume necessary data. Give neat and clean sketch (plan and section) to support your design. ## Short answer Designed open-well stair: floor-to-floor 3.12m, 22 risers at 141.8mm, tread 300mm, flight width 1.5m, going 3.0m, open well 0.5m, landing 1.5m×3.5m. ## Answer A **staircase** 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 reached 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. 6. **Landings:** provided at turns and between flights, with 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 the live load; fire-resistant material, 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 | Type | Description | |---|---| | Straight (single flight) | One continuous flight between two floors, no turn | | Quarter-turn | Direction changes by 90 degrees at a quarter landing | | Dog-legged | Two flights in opposite directions with a half-space landing, no well between flights | | Open-newel / open-well | Two or more flights with a clear well between them | | Half-turn (two-flight) | Turn of 180 degrees, either dog-legged or open-well | | Three-quarter turn | Three flights turning through 270 degrees around a well | | Bifurcated (branching) | One wide flight splits into two narrower flights at a landing | | Geometrical | Curved flights (circular or elliptical in plan) around an open well, without newel posts | | Circular / spiral (helical) | Wedge-shaped steps (winders) radiating from a central post; used where space is limited | ```text 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. For a public building the riser must not exceed 150 mm, so $3.12/0.15 = 20.8$ risers are needed; an even number, 22, is taken so that both flights are equal. #### 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 $R \le 150$ mm and tread $T = 300$ mm; flight width $b = 1.5$ m. #### Design 1. **Number of risers** $= H/R = 3.12/0.15 = 20.8$, adopt **22 risers**; exact riser $= 3.12/22 = 141.8$ mm ($\le 150$ mm, OK). 2. **Flights:** open-well (U-shaped) stair with two equal parallel flights joined by a landing at one end; each flight has 11 risers and 10 treads. 3. **Going of one flight** $= 10 \times 0.3 = 3.0$ 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 $= 11 \times 0.1418 = 1.56$ m. 6. **Length check:** $3.0 + 1.5 = 4.5$ m $\le 6$ m, so it fits; the spare 1.5 m is kept as entry/exit space. 7. **Check:** $2R + T = 2 \times 141.8 + 300 = 583.6$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 25.3^\circ$ (within 25-40 degrees). 8. **Waist slab:** effective span about 4.5 m, so depth $\approx$ span/20 $= 225$ 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 +------------------------+---------+ | FLIGHT 2 <<<<<< UP | | | 10 treads | LANDING | +- - - open well - - - - + | | FLIGHT 1 >>>>>> UP | | | 10 treads | | +------------------------+---------+ (arrows point up the stair) ``` ```text SECTION (not to scale) +---- upper floor 3.12 m _____| ____| flight 2 ______| landing +1.56 m ____| flight 1 _| ground floor +0.00 ``` #### Summary | Item | Adopted | |---|---| | Riser | 141.8 mm (22 nos.) | | Tread | 300 mm | | Flights | 2 flights x 11 risers | | Width of flight | 1.5 m | | Waist slab | 225 mm | **Answer: 22 risers of 141.8 mm and treads of 300 mm; 2 flights x 11 risers; flight width 1.5 m; open well 0.5 m.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. With ceiling height 3.0 m and floor slab 120 mm, what height H is used for the stair design? A. 3.00 m B. 2.88 m C. 3.12 m D. 3.24 m Answer: C. Floor-to-floor height = ceiling height + slab thickness = 3.0 + 0.12 = 3.12 m. (Key point: Floor-to-floor height) 2. Which type has two flights with a clear well between them? A. Open-newel / open-well stair B. Dog-legged stair C. Quarter-turn stair D. Straight stair Answer: A. Open-well stairs leave a clear well between flights, whereas a dog-legged stair has no well. (Key point: Types by plan shape) 3. For H = 3.12 m, R = 156 mm, b = 1.5 m and hall width 3.5 m, what results? A. 10 risers in total and a 0.5 m well B. 20 risers, 10 per flight with 9 treads, and a 0.5 m open well C. 20 risers, 10 per flight, and no well D. 24 risers and a 1.5 m well Answer: B. 3.12/0.156 = 20 risers; each flight has 10 risers and 9 treads; well = 3.5 - 2 x 1.5 = 0.5 m. (Key point: Risers and open well) 4. Which is correct for the open-well design (R = 156, T = 300, going 2.7 m, landing 1.5 m)? A. 2R + T = 612 mm, length 4.2 m fits in 6 m, waist slab span/20 about 210 mm, adopt 225 mm B. 2R + T = 456 mm, so the stair is too steep C. Length 4.2 m exceeds 6 m, so the stair does not fit D. Waist slab span/20 = 21 mm, adopt 25 mm Answer: A. 2(156) + 300 = 612 mm is within 550-650 mm; 2.7 + 1.5 = 4.2 m <= 6 m; depth about 4200/20 = 210 mm, adopt 225 mm. 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