Question

A welded plate girder of span 20 m is laterally restrained throughout its length. It has to carry a load of 90 kN/m over the whole span besides its self weight. If k = 200 and $f_y=250MPa$, then the thickness of web will be nearly

• A. $6\text{mm}$
• B. $8\text{mm}$
• C. $10\text{mm}$
• D. $12\text{mm}$

Answer 1

The correct option is B $8\text{mm}$

$\because$ Economical depth of plate girder is given by
$d={\left(\frac{Mk}{f_y}\right)}^{1/3}$
$M=\frac{w{l}^2}{8}=\frac{90\times {20}^2}{8}=4500kNm$
$\therefore d={\left(\frac{4500\times {10}^6\times 200}{250}\right)}^{1/3}=1532.62mm$
$\therefore$ Thickness of web, $t_w=\frac{d}{k}=\frac{1532.62}{200}=7.66\text{mm}$
So, provide $t_w=8\text{mm}$