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Structural Concrete - Hassoun

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702 Chapter 18 Stairs<br />

Figure 18.6<br />

Three- and four-stair flights.<br />

This type of stairs is favored by architects and sometimes called a pliers-shaped staircase<br />

or jackknife staircase.<br />

A study was made to determine the effect of the following parameters on the<br />

free-standing staircase forces and moments considering a live load of 100 psf (Figs. 18.10<br />

and 18.13):<br />

i. Width of stairs (Fig. 18.10): An increase in the width from 4 to 10 ft, will increase<br />

the forces and moments sharply. For example, the torsional moment along the flight<br />

increases by about 1400%. Therefore, it is desirable to restrict the flight width between<br />

4.0 and 6.0 ft. Other moments increase by about 450%.<br />

ii. Span length L: An increase in the span L will increase the forces and moments in the<br />

stair flight and landing significantly. For example, if L is increased from 8 to 16 ft, the<br />

shearing forces at the top edge of the stairs increases by about 230%. Moments increase<br />

by about 100 to 150%.

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