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Structural Concrete - Hassoun

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3.19 Analysis of Sections Using Tables 139<br />

Figure 3.37<br />

Sections of other shapes.<br />

5"<br />

4" 5"<br />

ε c = 0.003<br />

0.85f' c<br />

2"<br />

18.5"<br />

4"<br />

2.185"<br />

7.28" 6.185"<br />

N.A.<br />

C 1 '<br />

C 1 "<br />

4 + 2.185<br />

2<br />

= 5.10"<br />

C = 240 K<br />

2.5"<br />

4 # 9<br />

14"<br />

ε t = 0.004624 T = A s f y = 240 K<br />

Figure 3.38<br />

Example 3.13: (a) balanced and (b) underreinforced sections.<br />

= 0.85 × 4 × 14 × 2.185 = 104 K<br />

M n = C ′ 1<br />

(d − 2)+C′′<br />

1<br />

(d − 5.10)<br />

= 136 × 16.5 + 104 × 13.4 = 3637.6K⋅ in. = 303.1K⋅ ft<br />

3. Calculate φ M n ε t = 0.003(d t − c)/c, whered t = 18.5 in.:<br />

ε t = 0.003(18.5 − 7.28)∕7.28 = 0.004624 < 0.005 but > 0.004<br />

Since 0.004

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