Structural Concrete - Hassoun

698 Chapter 18 Stairs
The finishing on the stairs varies from troweling Alundum grits to adding asphalt tiles, terrazzo
tiles, marble, or carpets. In addition to dead loads, stairs must be designed for a minimum
live load of 100 psf.
18.2 TYPES OF STAIRS
There are different types of stairs, which depend mainly on the type and function of the building
and on the architectural requirements. The most common types are as follows.
1. Single-flight stairs: The structural behavior of a flight of stairs is similar to that of a one-way
slab supported at both ends. The thickness of the slab is referred to as the waist (Fig. 18.1).
When the flight of stairs contains landings, it may be more economical to provide beams at B
and C between landings (Fig. 18.2). If such supports are not provided, which is quite common,
the span of the staircase will increase by the width of two landings and will extend between
A and D. In residential buildings, the landing width is in the range of 4 to 6 ft, and the total
distance between A and D is about 20 ft.
An alternative method of supporting a single flight of stairs is to use stringers, or edge
beams, at the two sides of the stairs; the steps are then supported between the beams
(Fig. 18.3).
2. Double-flight stairs: It is more convenient in most buildings to build the staircase in double
flights between floors. The types commonly used are quarter-turn (Fig. 18.4) and closed- or
open-well stairs, as shown in Fig. 18.5. For the structural analysis of the stairs, each flight
is treated as a single flight and is considered supported on two or more beams, as shown
in Fig. 18.2. The landing extends in the transverse direction between two supports and is
designed as a one-way slab. In the case of open-well stairs, the middle part of the landing
carries a full load, whereas the two end parts carry half-loading only, as shown in Fig. 18.5d.
The other half-loading is carried in the longitudinal direction by the stair flights, sections A-A
and B-B.
3. Three or more flights of stairs: In some cases, where the overall dimensions of the staircase are
limited, three or four flights may be adopted (Fig. 18.6). Each flight will be treated separately,
as in the case of double-flight staircases.
4. Cantilever stairs: Cantilever stairs are used mostly in fire escape stairs, and they are supported
by concrete walls or beams. The stair steps may be of the full-flight type, projecting from
one side of the wall, the half-flight type, projecting from both sides of the supporting wall,
or of the semispiral type, as shown in Fig. 18.7. In this type of stairs, each step acts as a
cantilever, and the main reinforcement is placed in the tension side of the run and the bars are
anchored within the concrete wall. Shrinkage and temperature reinforcement is provided in
the transverse direction.
Another form of a cantilever stair is that using open-riser steps supported by a central
beam, as shown in Fig. 18.8. The beam has a slope similar to the flight of stairs and receives
the steps on its horizontally prepared portions. In most cases, precast concrete steps are used,
with special provisions for anchor bolts that fix the steps into the beam.
5. Precast flights of stairs: The speed of construction in some projects requires the use of precast
flights of stairs (Fig. 18.8). The flights may be cast separately and then fixed to cast-in-place
landings. In other cases, the flights, including the landings, are cast and then placed in position
on their supporting walls or beams. They are designed as simply supported one-way slabs