Question

A square beam laid flat is then rotated in such a way that one of its diagonal becomes horizontal. How is the moment capacity affected – 
1. Increases by 41.4%
2. Increases by 29.29% 
3. Decreases by 41.4%
4. Decreases by 29.29%

Answer 1

Correct Answer - Option 3 : Decreases by 41.4%

\(\frac{{{{\left( {Strength} \right)}_{Diamond}}}}{{{{\left( {Strength} \right)}_{Square}}}} = \frac{{{Z_{Diamond}}}}{{{Z_{Square}}}} = \frac{{\frac{{{a^3}}}{{6\sqrt 2 }}}}{{\frac{{{a^3}}}{6}}} = \frac{1}{{\sqrt {2\;} }} = \frac{1}{{1.414}}\)

That means strength of diamond (Square section keeping diagonal horizontal) is 41.4% less than strength of square.