--- title: "Staircase reinforcement drawing, effective span" subject: "Design of RCC Structure" chapter: 9 key: "semester_7/design_of_rcc_structure:staircase-reinforcement-drawing-effective-span" source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/staircase-reinforcement-drawing-effective-span site: BCT Engineering --- # Staircase reinforcement drawing, effective span Design of RCC Structure · Chapter 9: Design of slabs and staircase - Asked in: 2074 Asoj, 5+1 marks - Video: [Design of Reinforced Concrete Stairs](https://www.youtube.com/watch?v=KB2FXHb5Vck) — The Efficient Civil Engineer (by Dr. S. El-Gamal) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/staircase-reinforcement-drawing-effective-span - Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-9 ## Question Draw the typical reinforcement drawing for a flight and a landing of RCC staircase. Also define the effective span of staircase. ## Short answer Main bars run along the slope at bottom, distribution bars across; at re-entrant corner flight and landing bars are crossed and anchored Ld, not bent. Effective span: c/c between beams if supported at risers; going plus half landing width or 1 m (whichever smaller) at each end if landing spans across; c/c between supports if landing spans with stairs. ## Answer #### Typical reinforcement of a flight and landing A dog-legged or straight staircase flight is designed as a one-way slab spanning along the incline between supports (beams/walls or landing slabs). Main bars run along the slope at the bottom, and distribution bars are placed across them. Where the flight meets a landing at a re-entrant (internal) corner, the bars are not bent round the corner: the flight bars and the landing bars are crossed, and each is extended a distance $L_d$ beyond the corner. ```text SECTION THROUGH FLIGHT AND LANDING top landing flight ___________ / | distrib. | \ main bars / |-----------|---\---------/ <- steel at bottom, | main bars | \ / parallel to slope |___________| \_____/ support beam waist slab \ distribution bars @ 8 mm 200 c/c landing: main bars 10-12 mm @ 125-150 c/c bottom of flight bars turned up into landing (bars from flight and landing cross at the re-entrant corner, both anchored for Ld) ``` Points to show on the drawing: - Main bars along the slope at the bottom, bent at the ends to give anchorage into the supporting beam or wall. - Distribution bars (8 mm @ 200 c/c) tied on top of the main bars. - Top steel (about 50% of the bottom steel) at the supports if the ends are partly fixed. - At a re-entrant (internal) corner, the tension bars must not be bent round the corner, because the bar would try to straighten and push off the cover; bars from the flight and the landing are crossed and anchored separately. - Cover 15-20 mm; bar marks, diameter and spacing written on the drawing. #### Effective span of a staircase (IS 456 cl. 33.1) For stairs spanning along their length (without stringer beams), the effective span is taken as: 1. Where the stairs are supported at the top and bottom risers by beams spanning parallel with the risers: the **centre-to-centre distance between the beams**. 2. Where the stairs span on to the edge of a landing slab that spans parallel with the risers (at right angles to the stairs): the **going of the stairs plus, at each end, either half the width of the landing or 1 m, whichever is smaller**. 3. Where the landing slab spans in the same direction as the stairs: the stairs and landing act together as a single slab, and the span is the **centre-to-centre distance between the supporting beams or walls**, with the going measured horizontally. For a stair slab spanning across its width (between side walls or stringer beams), the effective span is taken as for an ordinary slab: clear span plus effective depth, or centre-to-centre of supports, whichever is smaller. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Where are the main bars placed in the flight? A. At the top, perpendicular to the slope B. At the bottom, parallel to the slope C. In the steps only D. At mid-depth Answer: B. The flight acts as a one-way slab spanning along the incline, so tension steel is at the bottom along the slope. (Key point: Position of main bars) 2. Why must tension bars not be bent round a re-entrant corner? A. It is harder to bend B. The resultant force would push off the cover, so bars are cut and anchored separately C. It reduces steel area D. It increases the span Answer: B. A bent tension bar tries to straighten, breaking out the concrete cover at the internal corner. (Key point: Re-entrant corner) 3. When the stair spans onto a landing slab spanning in the same direction, the effective span is: A. Going only B. Going plus at each end half the landing width or 1 m, whichever is smaller C. Going plus 2 m at each end D. Clear span plus d Answer: B. IS 456 cl. 33.1 gives going plus, at each end, the smaller of half the landing width or 1 m. (Key point: Effective span rule 2) 4. What is the role of distribution bars (8 mm @ 200 c/c)? A. They carry the main bending moment B. They are placed across the main bars, holding them in place C. They resist torsion at corners D. They replace the stirrups Answer: B. They are tied above and across the main bars to keep them in position and control shrinkage cracking. 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