Concept: Clause 33.1 of IS 456:2000 gives us the guideline to calculate the effective span of a stair 'where spanning on to the edge of a landing slab, which spans parallel, with the risers, a distance equal to the going of the stairs plus at each end either half the width of the landing or one meter, whichever is smaller.' Calculation: Given: Going of stair = 2.2 m half width of landing = 2.5 / 2 = 1.25 m > 1 m ∴ adopted legth for calculation of effective span = 1 m ∴ Effective span of stair = 2.2 + 1 + 1 = 4 m Important Points Some frequent stair types and their effective spans are given below Span type Effective Span Where supported at top and bottom risers by beams spanning parallel with the risers The distance center-to-center of beams. Where spanning on to the edge of a landing slab, which spans parallel, with the risers A distance equal to the going of the stairs plus at each end either half the width of the landing or one metre, whichever is smaller Where the landing slab spans in the same direction as the stairs, they shall be considered as acting together to form a single slab. The span determined as the distance centre-to-centre of the supporting beams or walls, the going being measured horizontally.