In Limit state Method of design, the maximum strain in steel at failure is : 

(Adopting standard notations) 

Explanation:

The following are the assumptions of the design of flexural members employing limit state of collapse:
(i) Plane sections normal to the axis remain plane after bending.
(ii) The maximum strain in concrete at the outer most compression fibre is taken as 0.0035 in bending. (iii) The acceptable stress-strain curve of concrete is assumed to be parabolic as shown in figure below:

(iv) The tensile strength of concrete is ignored.
(v) The design stresses of the reinforcement are derived from the representative stress-strain curves as shown in figure below:

Partial safety factor for steel and concrete should be considered as 1.15 and 1.5 respectively.

(vi) The maximum strain in the tension reinforcement in the section at failure shall not be less than

  \(\frac{f_{y}}{1.15 E_{s}}+0.002\)

Where f, is the characteristic strength of steel and Es = modulus of elasticity of steel.