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Structural Concrete - Hassoun

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646 Chapter 17 Design of Two-Way Slabs<br />

10 no. 5<br />

Total 20 no. 5<br />

10 no. 5<br />

10 no. 5 10 no. 5 10 no. 5<br />

Total 10 no. 4<br />

10 no. 4<br />

5 no. 4<br />

10 no. 4<br />

5 no. 4<br />

10 no. 4<br />

9 no. 5 9 no. 5<br />

Total 18 no. 5<br />

10 no. 5 10 no. 5<br />

10 no. 5<br />

Total 14 no. 4<br />

14 no. 4<br />

7 no. 4 14 no. 4 7 no. 4<br />

14 no. 4<br />

Figure 17.20 Example 17.3: Reinforcement details. For bar length, refer to Fig. 17.16.<br />

long direction. Therefore, d(longdirection) =9.0 − 0.75 − 5 = 7.9in. and d (shortdirection) =<br />

16<br />

9.0 − 0.75 − 5 − 5 −=7.3 in. For practical applications, an average d = 9 − 1.5 = 7.5 in. can be<br />

8 16<br />

used for both directions.<br />

The design procedure can be conveniently arranged in a table form, as in Tables 17.7 and 17.8.<br />

The details for the bars selected for this interior slab are shown in Fig. 17.20 using the straight<br />

bar system. Minimum lengths of the bars must meet those shown in Fig. 17.16.<br />

Straight bars and f y = 60 ksi steel bars are more often preferred by contractors.<br />

width of panel<br />

Maximum spacing = = 168 = 12 in.<br />

no. of bars 14<br />

occurs at the middle strip in the short direction; this spacing of 12 in. is adequate because it is less<br />

than 2h = 18 in. and less than 18 in. specified by the ACI Code. Note that all steel ratios are less<br />

than ρ max = 0.018. Thus φ = 0.9.

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