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Structural Concrete - Hassoun

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17.6 Minimum Slab Thickness to Control Deflection 623<br />

Solution<br />

1. For corner panel no. 1, the minimum thickness is l n /30 (f y = 60 ksi, and no edge beams are used;<br />

see Table 17.1).<br />

l n1<br />

= 24 − 20 = 22.33 ft (long direction)<br />

12<br />

22.33 × 12<br />

Min. h = = 8.93 in. say, 9.0in.<br />

30<br />

2. For the interior panel no. 3 and f y = 60 ksi, the minimum slab thickness is l n /33 = (22.33 × 12)/<br />

33 = 8.12 in., say, 8.5 in. is used for all panels, then h = 9.0 in. will be adopted.<br />

Example 17.2<br />

The floor system shown in Fig. 17.7 consists of solid slabs and beams in two directions supported on<br />

20-in. square columns. Using the ACI Code equations, determine the minimum slab thickness required<br />

for an interior panel. Use f c ′ = 3ksiandf y = 60 ksi.<br />

Solution<br />

1. To use Eq. 17.1, α m should be calculated first. Therefore, it is required to determine I b , I s ,andα f<br />

for the beams and slabs in the long and short directions.<br />

Figure 17.7 Example 17.2.

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