Question

A prestressed concrete rectangular beam of size 300 mm x 900 mm is prestressed with an initial prestressing force of 700 kN at an eccentricity of 350 mm at midspan. Stress at top due to prestress alone, in N/mm${}^2$ is

• A. - 3.46 (tension)
• B. 2.59 (compression)
• C. zero
• D. 8.64 (compression)

Answer 1

The correct option is A - 3.46 (tension)



Stress at top

$=\frac{P}{A}-\frac{Pe}{Z}$

$=\frac{700\times {10}^3}{300\times 900}-\frac{700\times {10}^3\times 350}{\frac{300\times {900}^2}{6}}$

$=-3.46N/m{m}^2\left(tension\right)$