Concept: The ratio of limiting depth of neutral axis to the effective depth of the beam is given by
xu
d
=
Maxstrainconcrete
Gradeofsteel
ModulusofElasticityofsteel×F.O.S
+0.002+Maxstrainconcrete
Note: We know the standard values of the ratio of limiting depth of neutral axis to the effective depth (k) of the beam for different steel sections as following: xu = k × d
Grade of Steel
Fe 500
Fe 415
Fe 250
‘k’ value
0.46
0.48
0.53
∴ For Fe415 grade limiting value of depth of neutral axis is 0.48 × d