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Structural Concrete - Hassoun

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CHAPTER18<br />

STAIRS<br />

Office building under construction, Chicago, Illinois.<br />

18.1 INTRODUCTION<br />

Stairs must be provided in almost all buildings, either low-rise or high-rise buildings, even if adequate<br />

numbers of elevators are provided. Stairs consist of rises, runs (or treads), and landings. The<br />

total steps and landings are called a staircase. Therise is defined as the vertical distance between<br />

two steps, and the run is the depth of the step. The landing is the horizontal part of the staircase<br />

without rises (Fig. 18.1).<br />

The normal dimensions of the rises and runs in a building are related by some empirical rules:<br />

Rise + run = 17in. (431mm)<br />

2 × rise + run = 25in. (635mm)<br />

Rise × run = 75in. 2 (0.05m 2 )<br />

The rise depends on the use of the building. For example, in public buildings the rise is about<br />

6 in., whereas in residential buildings it varies between 6 and 7.5 in. The run is about 1 ft in public<br />

buildings and varies between 9 and 12 in. in residential buildings. In general, a rise should not<br />

exceed 8 in. or be less than 4 in., and the number of rises is obtained by dividing the structural<br />

floor-to-floor dimension by the assumed rise.<br />

696

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