Chapter 16

Stairs

Stairs not infrequently form one of the most prominent visual features of a building, and

as such present a challenge to both engineer and architect. Unlike the normal floor or roof

slab where a slight reduction in thickness can seldom be seen, the provision of stairs

having the maximum possible slenderness is often visually desirable, making a vast

difference between clumsiness and grace. Any consequent increase in the amount of

reinforcement required to compensate for restricting the effective depth to the minimum

possible value is insignificant in relation to that required for the building as a whole, and

is clearly outweighed by the enhanced appearance achieved.

Many types of stair design can be utilized, ranging from a simple flight spanning

between supporting beams, to free-standing scissor flights with landings not

independently supported, and helicoidal stairs turning through 360 and supported at top

and bottom only.

Figure 16.1 Stairs.

Advice on the analysis of the simplest types only is given in BS8110. To analyse

more-complex designs, reference must be made to the many specialist articles that have

appeared: see, for example, refs 2426 (design information drawn from these references

is given in RCDH).

The normal terms used in describing stairs, listed in Allen, are shown in Figure 16.1a,

together with the commonly adopted limiting dimensions. To reduce the waist thickness

to the minimum, if a reasonable thickness of finish is to be applied to the concrete it is

possible to adopt the concrete profile shown in Figure 16.1b, although such an

arrangement is clearly slightly more difficult to form and concrete. The rules for

slenderness given in BS8110 will normally determine the minimum waist thickness that

can be used. Note that, provided the length of flight forms not less than 60% of the span,