UNIT 8

Prepared by Dr. Prashanth J. Page 1

UNIT 8: DESIGN OF STAIRCASES

8.1 INTRODUCTION

Staircase flights are generally designed as slabs spanning between wall supports or landing

beams or as cantilevers from a longitudinal inclined beam. The staircase fulfils the function

of access between the various floors in the building. Generally, the flight of steps consists of

one or more landings provided between the floor levels.

Fig. 1: Terms used in the staircase

The structural components of a flight of stairs comprises of the following elements,

a) Tread: The horizontal portion of a step where the foot rests is referred to as tread. 250

mm to 300 mm is the typical dimensions of a tread.

b) Riser: Riser is the vertical distance between the adjacent treads or the vertical

projection of the step with the value of 150 to 190 mm depending upon the type of

building. The width of stairs is generally 1 to 1.5 m and in any case not less than 850

mm. Public buildings should be provided with larger widths to facilitate free passage

to users and prevent overcrowding.

c) Going: Going is the horizontal projection (plan) of an inclined flight of steps between

the first and last riser. A typical flight comprises of two landings and one going as

shown in Fig. 2 (e). To break the monotony of climbing, the number of steps in a

flight should not generally exceed 10 to 12.

The tread-riser combination can be provided in conjunction with

i) Waist slab (Fig. 2 (a))

ii) Tread-riser type (continuous folded plate) (Fig. 2 (b))

iii) Isolated cantilever tread slab (Fig. 2 (c))

iv) Double cantilever precast tread slab with a central inclined beam (Fig. 2 (d)).


Fig. 2: Typical flight in a staircase

8.2 TYPES OF STAIRCASES

Aesthetic considerations have evolved a wide variety of staircases over the years. Some of

the common geometrical configurations used are compiled in Fig. 3.

a) Single flight staircase: A typical single flight stairs is shown in Fig. 3 (a). This

type is used in cellars or attics where the height between floors is small and the

frequency of its use is less.

b) Single or quarter turn staircase: Fig. 3 (b) shows the plan arrangement of single

right angled turn staircase. The staircase flight generally runs adjoining the walls

and provides uninterrupted space at the centre of the room. Generally used in

domestic houses where floor heights are limited to 3 m.

c) Dog legged staircase: The most common type of stairs arranged with two adjacent

flights running parallel with a mid landing as shown in Fig. 3 (c). Where space is

at a premium, dog legged staircase is generally adopted resulting in economical

utilization of available space.

d) Open well staircase: In public buildings where large spaces are available, open

well staircase shown in Fig. 3 (d) is generally proffered due to its better


accessibility, comfort and ventilation due to its smaller flights with an open well at

the centre.

e) Spiral staircase: In congested locations, where space available is small, spiral

stairs are ideally suited. A typical spiral staircase shown in Fig. 3 (e) comprises a

central post with precast slab treads anchored to the central column. It is not user

friendly due to the reduced tread width near the port and is suitable only for single

person to use the staircase at a time.

Fig. 3: Various types of staircases


8.3 LOADS ON STAIRCASES

The loads to be considered in the design of staircases comprise of following types.

a) Dead loads: The various dead loads are,

i) Self weight of stair slab concrete which includes the waist slab, tread-riser etc.

ii) Self weight of finishes (0.5 to 1 kN/m2)

b) Live loads: The IS: 875-1987 (part II) code specifies the live loads to be considered

as uniformly distributed load of intensity 5 kN/m2 for public buildings and 3 kN/m

2

for residential buildings where the specified floor loads do not exceed 2 kN/m2, and

the staircases are not liable for over crowding.

8.4 EFFECTIVE SPAN OF STAIRS

When the stair flight is supported at the ends by landing beams, the effective span is

projected horizontal distance between the centre lines of the landing beams.

The effective span of stairs without stringer beam shall be taken as the following horizontal

distances as per IS: 456 code Cl. 33.1.

a) Where supported at top and bottom risers by beams spanning parallel with the risers,

the distance centres to centre of beams.

b) Where spanning on to the edge of a landing slab, which spans parallel with the risers

(as shown in Fig. 4), 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.

c) Where the landing slab spans in the same direction as the stairs, they shall be

considered as acting together to form a single slab and the span determine as the

distance centre to centre of the supporting beams or walls, the going being measured

horizontally.

Fig. 4: Effective span of stairs (IS: 456 2000)


8.5 DISTRIBUTION OF LOADING ON STAIRS

The distribution of loads on stairs and landing slabs depends upon the type of spanning of the

stair flight and the landing slab.

In the case of stairs with open walls, where span partly crossing at right angles occur, the load

on areas common to any two such spans may be taken as one half in each direction as shown

in Fig. 5. Where flights or landings are embedded into walls for a length of not less than 110

mm, are designed to span in the direction of flight, a length of 150 mm strip may be deducted

from the loaded area and the effective breadth of the section increased by 75 mm for purposes

of design.

Fig. 5: Distribution of loads on stairs (IS: 456 2000)

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