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Structural Concrete - Hassoun

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752 Chapter 19 Introduction to Prestressed <strong>Concrete</strong><br />

Figure 19.6b<br />

Example 19.4: Tendon profile.<br />

Figure 19.6c Example 19.4: Average e 2 .<br />

3. Limits of the eccentricity e at midspan section: Calculate the allowable stresses and moments.<br />

At transfer, f ′ ci = 4000 psi, f ci = 0.6 × 4000 = 2400 psi, and f ti = 3√ f c ′ = 190 psi. At service load,<br />

f c ′ = 5000 psi, f c = 0.45, f c ′ = 2250 psi, and f t = 6√ f c ′ = 424 psi.<br />

Self − weight of beam = 372 × 150 = 388 lb∕ft<br />

144<br />

M D (self − weight) = 0.388<br />

8 (48)2 × 12 = 1341 K ⋅ in.<br />

M a<br />

(additional load and live load) = w a L2<br />

8<br />

0.9 + 1.1<br />

= (48) 2 × 12 = 6912 K ⋅ in.<br />

8<br />

Total moment (M T )=M D + M a = 8253 K ⋅ in.<br />

F i = stress at transfer × area of prestressing steel

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