Staircase reinforcement drawing, effective span

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.

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.