Question

A simply supported rolled steel joist of I-section has flange width 250 mm and overall depth 600 mm. Its moment of inertia $I_{xx}=12\times {10}^{8}m{m}^4$. The steel joint is used as a beam over a simply supported span of 6 m. It carries a load of 40 kN/m including its self weight throughout the span. The maximum stress induced in the beam in $N/m{m}^2$ due to bending would be

• A. 30
• B. 90
• C. 45
• D. 60

Answer 1

The correct option is C 45

$\frac{f}{y}=\frac{M}{I}$

$\Rightarrow f=\frac{M}{Z}$

Where
$Z=I/y=\frac{12\times {10}^8}{300}m{m}^3$

$=4\times {10}^{6}m{m}^3$

$M=\frac{W{I}^2}{8}=40\times \frac{6^2}{8}=180kN-m$

$=\frac{180\times {10}^6}{4\times {10}^6}=45N/m{m}^2$