Question

A simply supported beam is loaded by a couple of 1500 N-m as shown in figure. The beam has a channel type cross section. The maximum tensile stress in the beam is ______MPa

• A. 2.8
• B. 3.8
• C. 1.8
• D. 4.8

Answer 1

The correct option is A 2.8

The location of centroid from the bottom fibre is

$\overline{y}=\frac{(6\times 15)\times 7.5+(30\times 3)\times 1.5}{(6\times 15)+(30\times 3)}=4.5cm$

$\therefore I=3375c{m}^4$

$y_{max}=15-4.5=10.5cm=0.105m$

Bending moment diagram



$\therefore f_{max}=\frac{M}{I_{N.A}}.y_{max}=\frac{900\times 0.105}{3375\times {10}^{-8}}=2.8MPa$