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Question 15.18: Refer to the problem in Example 15.17. Determine directly th...

Refer to the problem in Example 15.17. Determine directly the ultimate and the allowable loads using N_{\text {cor }}. All the other data remain the same.

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UseEq. (15.49a)

 

Q_{u}( kip )=Q_{b}+Q_{f}=0.80 N_{c o r}(L / d) A_{b}+0.04 \bar{N}_{c o r} A_{s} (15.49a)

 

Q_{u}=Q_{b}+Q_{f}=0.8 N_{c o r}(L / d) A_{b}+0.04 \bar{N}_{c o r} A_{s}( kips )

 

Given: N_{c o r}=21, \bar{N}_{c o r}=15, d=16 in , L=41 ft

 

A_{b}=\frac{3.14}{4} \frac{16}{12}^{2}=1.39 ft ^{2} ; A_{s}=3.14 \times \frac{16}{12} \times 41=171.65 ft ^{2}

 

Substituting

 

Q_{b}=0.80 \times 21 \frac{41}{1.33} \times 1.39=720 \leq 8 N_{c o r} A_{b} \text { kips }

 

Q_{b l}=8 \times 21 \times 1.39=234 kips

 

The limiting value of Q_{b}=234 \text { kips }

 

\begin{aligned}&Q_{f}=0.04 N_{c o r} A_{s}=0.04 \times 15 \times 171.65=103 kips \\&Q_{u}=Q_{b}+Q_{f}=234+103=337 kips \\&Q_{a}=\frac{337}{4}=84 kips\end{aligned}

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