Question

The cross-section of a beam is shown in figure -I. Its $I_{xx}$ is equal to $3\times {10}^{6}m{m}^4$. It is subjected to a load as shown in figure-II. The maximum tensile stress in the beam would be :

• A. indeterminable as data is insufficient
• B. $21MN/m^2$
• C. $21kN/m^2$
• D. $21NN/m^2$

Answer 1

The correct option is B $21MN/m^2$

BMD of beam


Upper fibres of the beam will be under tension since the maximum BM of 0.9 kN-m is hogging in nature. The maximum tensile stress

$f=\frac{M{y}_1}{I_{xx}}=\frac{0.9\times {10}^6\times 70}{3\times {10}^6}$

$=\frac{9\times 7}{3}=21N/m{m}^2=21MN/m^2$