Question

A beam of symmetrical I-section, made of structural steel has an overall depth of 300 mm. If the flange stresses developed at the top and bottom of the beam are $1200kg/c{m}^2$ and $300kg/c{m}^2$ respectively, then the depth of neutral axis from the top of the beam would be

• A. 250 mm
• B. 240 mm
• C. 200 mm
• D. 180 mm

Answer 1

The correct option is B 240 mm

The variation of stresses in bending is shown below.

From rule of similar triangles, we have

$\frac{x}{1200}=\frac{300-x}{300}$

$\Rightarrow x=1200-4x$

$\Rightarrow x=\frac{1200}{5}=240mm$