Structural Concrete - Hassoun

9.7 One-Way Joist Floor System 337
2 no. 5
Figure 9.8 Example 9.6.
The rib carries a load from (20 + 4)-in.-wide slab plus its own weight:
U = 24 × 185 +(1.2 × 52) =432.4 lb∕ft
12
M u = UL2
8
= 0.4324 (20) 2 × 12 = 259.4 K⋅ in.
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Rectangular steel pans used in one-way ribbed slab construction.
3. Design of rib: The total depth is 12 in. Assuming no. 5 bars and concrete cover of 3 in., the
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effective depth d is 12 − 3 − 5 = 10.9 in. Check the moment capacity of the flange (assume
4 16
tension-controlled section, φ = 0.9):
(
φM n (flange) =φC d − t )
where C = 0.85f c ′ 2
bt
(
M u = 0.9(0.85 × 4 × 24 × 2) 10.9 − 2 )
= 1454 K ⋅ in.
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