Steel Staircase

35.3 STEEL STAIRS

Stairs in public buildings are generally constructed of steel or concrete. Because steel stairs can be shop fabricated and brought to the site ready for installation, they are far more commonly used than concrete stairs. Another reason for the lack of use of concrete stairs is that their formwork is complicated and expensive. Prefabricated steel stairs are used in all types of public buildings, that is, steel- and concrete-frame  buildings and load-bearing load-bearing masonry buildings. They They are particularly particularly popular  for exit stairs.

A typical prefabricated flight of a steel stair consists of two stringer beams (stringers) to which tread-riser units made of sheet steel are welded, Figure 35.13 . The tread pan is generally site filled with concrete, Figure 35.14 . For good wear resistance, a concrete strength of 5,000 psi is generally specified. Other tread finishes include a  precast-concrete drop-in tread with a slip-resistant broom finish, Figure 35.15 (a), and sheet steel with a raised, diamond-shaped checkered pattern, Figure 35.15 (b). Factory-installed epoxy-aggregate fill or wear- and slip-resistant coatings can also be used.

STRINGERS

Stringers in a steel stair function as inclined beams, spanning from the floor to the landing and from the landing to the next floor. They generally consist of a structural-steel channel.

LANDING FRAME

The landing of a steel stair is generally framed with structural steel members as a unit, called a landing frame . Typical details of connections between stringers and landings are shown in Figure 35.18 . The finish on the landing is generally the same as that on the treads. Thus, where site-cast concrete is used on treads, the landing is also topped with concrete. The landing frame may be supported on a beam (specially introduced for the purpose) between the upper  and lower floors of the building, on (masonry or concrete) stair-enclosure walls, or on columns independent of the structural frame of the building. In most  buildings, however, the landing frame for a prefabricated steel stair is supported by suspending it from the upper-level floor beams with steel hanger bars, Figure 35.19 . A major advantage of a suspended landing is that it allows adjustment of the height of  the landing with a few turns of the nuts. Additionally, the entire stair can be erected before constructing the walls of the stair enclosure.