Question

A prestressed concrete beam has a cross-section with the following properties :
$AreaA=46400m{m}^2,I=75.8\times {10}^{7}m{m}^4$, $Y_{bottom}=244mm,Y_{top}=157mm$.
It is subjected to a prestressing force at an eccentricity 'e' so as to have a zero stress at the top fibre. The value of 'e' given by

• A. 66.66 mm
• B. 66.95 mm
• C. 104.72 mm
• D. 133.33 mm

Answer 1

The correct option is C 104.72 mm


Hence for zero stress at top ,

$\frac{P}{A}=\frac{Pe{Y}_{top}}{I}$

$\frac{1}{46400}=\frac{e\times 156}{75.8\times {10}^7}$

e = 104.72 mm