Question

A concrete beam of rectangular cross-section of $200mm\times 400mm$ is prestressed with a force of 400 kN at an eccentricity of 100 mm. The maximum compressive stress in the concrete is

• A. $12.5N/m{m}^2$
• B. $7.5N/m{m}^2$
• C. $5.0N/m{m}^2$
• D. $2.5N/m{m}^2$

Answer 1

The correct option is A $12.5N/m{m}^2$

The maximum compressive strength in concrete is given by
${\sigma }_{max}=\frac{P}{A}+\frac{Pey}{I}=\frac{400\times {10}^3}{200\times 400}+\frac{400\times {10}^3\times 100\times 6}{200\times {400}^2}=5+7.5N/m{m}^2=12.5N/m{m}^2$