Which of the following statements are incorrect?
Which of the following statements are incorrect?
A. In reinforced cement concrete, modular ratio is defined by the ratio (Modulus of elasticity of steel / modulus of elasticity of concrete)
B. Modulus of rupture of cement concrete is directly proportional to the permissible compressive stress in concrete.
C. In reinforced cement concrete, modular ratio is defined by the ratio (Modulus of elasticity of Concrete / modulus of elasticity of Steel)
D. The characteristics compressive strength of M20 grade cement concrete at 7 days is 20 N/mm<span style="position: relative; line-height: 0; vertical-align: baseline; top: -0.5em;">2</span>
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Right Answer is:
SOLUTION
Concept:
In WSM:
i) As per IS 456:2000, the Modular ratio of concrete is given by:
\(m = \frac{{280}}{{3{\sigma _{cbc}}}}\)
Where,
σcbc = permissible compressive stress in concrete.
Therefore, the modular ratio of concrete is inversely proportional to the permissible compressive stress in concrete.
ii) In LSM:
Modular ratio,
In reinforced cement concrete, the modular ratio is defined by the ratio (Modulus of elasticity of steel/modulus of elasticity of concrete)
\({\rm{m}} = \frac{{{{\rm{E}}_{{\rm{st}}}}}}{{{{\rm{E}}_{\rm{c}}}}}\)
where Est and Ec are modulus of elasticity of steel and concrete respectively.
Important points:
A modular ratio is used to find out the equivalent area required by one material with respect to other material for the same strength.
The modular ratio represents relative strength between two materials
iii) The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days (fck).
The characteristic strength is defined as the strength of the concrete below which not more than 5% of the test results are expected to fall.