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Structural Concrete - Hassoun

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19.1 Prestressed <strong>Concrete</strong> 727<br />

f ′ c<br />

Use b = 12 in., h = 24 in., normal-weight concrete with f c ′ = 4500 psi, and an allowable<br />

= 2050 psi.<br />

Solution<br />

1. Stresses due to dead and live loads only are the self-weight of the beam = (1 × 2) × 150<br />

= 300 lb/ft:<br />

dead − load moment M DL = wL2 = 0.300(24)2 = 21.6K⋅ ft<br />

8 8<br />

Stresses at the extreme fibers are<br />

σ = Mc<br />

I<br />

σ D =<br />

= M(h∕2)<br />

bh 3 ∕12 = 6M<br />

bh 2<br />

6 × 21.6 × 12, 000<br />

12(24) 2 =±225 psi<br />

Figure 19.2 Example 19.1.

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