Question

12.2.b △l = \frac{p×l}{a×e}
a = 8×8 = 7.5 in×7.5 in = 56.25 in² (nominal)
l = 12 ft = 144 in
p = 45 kips = 45,000 lb
e = 1,600,000 psi
\frac{45,000 lb×144 in}{56.25 in²×1,600,000 psi}=

Explanation:

Step1: Identify given values

$P = 45000\ lb$, $A=56.25\ in^{2}$, $L = 144\ in$, $E=1600000\ psi$

Step2: Substitute values into formula

$\Delta L=\frac{P\times L}{A\times E}=\frac{45000\times144}{56.25\times1600000}$

Step3: Calculate the result

$\Delta L=\frac{45000\times144}{56.25\times1600000}=\frac{6480000}{90000000}= 0.072\ in$

Answer:

$0.072\ in$