The following steps should be followed to design a double reinforcement Beam-
Step 1:
Determine the limiting moment of resistance for the given c/s(Mulim) using the equation for singly reinforced beam
Mulim = 0.87.f y .Ast1 .d [1 – 0.42X umax]
Or
Balanced section
Ast1 = (0.36.f ck.b.X umax)/(0.87fy)
Step 2
If factored moment M u > Mulim , then doubly reinforced beam is required to be designed for additional moment.
Mu – Mulim = fsc.A sc (d – d’) [f sc
value from page no. 70]
Step 3
Additional area of tension steel Ast 2
Ast 2 =Asc.fsc/0.87fy
Step 4 :
Total tension steel Ast, Ast = Ast 1 + Ast 2
