Under working stress design method of concrete structures, calculate the modular ratio of M20 grade concrete subjected to compressive stress due to bending, if the permissible compressive stress for M20 grade concrete in bending is 7 N/mm².

Concept:

According to the work stress method:

\(Modular\, ratio\,(m)={280\over 3σ_{cbc}}\)

Where σ_cbc = compressive strength of concrete.

Calculation:

Given

Grade of concrete M20

Permissible compressive stress (σ_cbc) = 7 N/mm²

Modular ratio (m) = \({280\over 3σ_{cbc}}={280\over 3\times 7}=13.33\)

Modular ratio (m) = 13.33

Hence option (2) is correct.