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Building Design and Construction Handbook - Merritt - Ventech!

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FIGURE 16.5 Reinforced concrete stairs.<br />

16.3.10 Concrete Stairs<br />

VERTICAL CIRCULATION 16.11<br />

Depending on the method of support provided, concrete stairs may be designed as<br />

cantilevered or inclined beams <strong>and</strong> slabs (Fig. 16.5). The entire stairway may be<br />

cast in place as a single unit, or slab or T beams may be formed first <strong>and</strong> the steps<br />

built up later. Soffits formed with plywood or hardboard forms may have a smoothenough<br />

finish to make plastering unnecessary. Concrete treads should have metal<br />

nosings to protect the edges. Stairs also may be made of precast concrete.<br />

16.4 ESCALATORS<br />

Escalators, or powered stairs, are used when it is necessary to move large numbers<br />

of people from floor to floor. They provide continuous movement of persons <strong>and</strong><br />

can thus remedy traffic conditions that are not readily addressed by elevators. Escalators<br />

should be viewed as preferred transportation systems whenever heavy traffic<br />

volumes are expected between relatively few floors. Escalators are used to connect<br />

airport terminals, parking garages, sports facilities, shopping malls, <strong>and</strong><br />

numerous mixed-use facilities.<br />

Although escalators generally are used in straight sections (Fig. 16.6), spiral<br />

escalators (Fig. 16.7) also are available. Although expensive due to manufacturing<br />

complexities, they offer distinct advantages to both the designer <strong>and</strong> user because<br />

of their unique semicircular plan form.<br />

16.4.1 Components of an Escalator<br />

An escalator resembles a powered ramp in construction (Art. 16.2). The major<br />

difference is that a powered ramp has a continuous treadway for carrying passengers,<br />

whereas the treadway of an escalator consists of a series of moving steps. As<br />

for a powered ramp, the installation of powered stairs should conform with the<br />

requirements of the ‘‘American National St<strong>and</strong>ard Safety Code for Elevators,<br />

Dumbwaiters, Escalators <strong>and</strong> Moving Walks,’’ ANSI A17.1.<br />

An escalator consists of articulated, grooved treads <strong>and</strong> risers attached to a continuous<br />

chain moved by a driving machine <strong>and</strong> supported by a steel truss framework

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