Question

What is the modular ratio to be used in the analysis of RC beams using working stress method if the grade of concrete is M20?

• A. 18.6
• B. 13.3
• C. 9.9
• D. 6.5

Hint:

For working stress method, always use the modified modular ratio based on permissible concrete stress.

Answer 1

The Correct Option is B

Step 1: Formula for modular ratio.
In working stress method, the modular ratio is given by:
\[ m = \frac{280}{3 \sigma_{cbc}} \]
Step 2: Permissible stress for M20 concrete.
For M20 concrete, permissible compressive stress in bending is:
\[ \sigma_{cbc} = 7 \text{ N/mm}^2 \]
Step 3: Substitute the value.
\[ m = \frac{280}{3 \times 7} = \frac{280}{21} = 13.33 \]
Step 4: Conclusion.
Thus, the modular ratio to be used is approximately 13.3.