Detailing of reinforcement in staircases

Detailing of a staircase means the arrangement of bars in the flight and landing so that the tensile stresses are resisted, the bars are properly anchored, and the cover and spacing are as per IS 456.

Flight (waist slab)

• Main bars are placed at the bottom of the waist slab, parallel to the slope, usually 10 or 12 mm diameter at 100-150 mm c/c. They run to the supports and are anchored for the full development length $L_d$, with a bend if there is little space.
• Distribution bars (8 mm @ 150-200 c/c) are placed perpendicular to the main bars to hold them in place and resist shrinkage and temperature stresses; minimum steel is 0.12% of the gross area for HYSD bars (Fe415/Fe500).
• Top (negative) steel: where the flight is built into a wall or beam, or is continuous over a landing, top bars of about 50% of the mid-span steel are placed over the support and extended $0.1 l$ to $0.3 l$ into the span.
• The thickness of the waist slab is measured perpendicular to the slope; the steps themselves are not counted as structural.

Landing

• The landing is an ordinary slab; its main bars span in the direction in which the landing spans, and bars from the flight are carried into it for anchorage.
• When the flight and landing are in different planes, the bars at the re-entrant corner are not bent continuously round it. Both sets of bars are crossed, and each is extended $L_d$ beyond the intersection, because a bent tension bar would try to straighten and break out the concrete cover.

          landing           flight
   ____________________
  |   ____________    \
  |  |  main bars  \   \  distribution
  |__|______________\___\ bars across
     <-- Ld --> crossing bars at the
                 internal corner

General rules

• Minimum cover 15-20 mm (mild exposure); spacing of main bars not more than $3d$ or 300 mm, and of distribution bars not more than $5d$ or 300 mm.
• In a dog-legged stair, the bars of the two flights are lapped or anchored where they meet the common landing.
• Stirrups are not required in the slab when $\tau_v \le k\tau_c$.