DESIGN OF CORBELS
Check a/d < 1
(else, it is probably a shallow or deep beam)
Step 1. Find factored shear Vu and tensile force Nuc
If Nuc is not specified, use a minimum value of Nuc = 0.2 Vu (ACI 11.9.3.4)
Compute nominal values of shear and tensile force
Vn = Vu / 0.85 ;
Nnc = Nuc / 0.85
If Vn > 0.2 fc’ b d OR
Vn > 800 b d (lb. units)
then section size is inadequate (ACI 11.9.3.2)
Step 2. Compute shear-friction reinforcement (ACI 11.7.4.1)
Avf 
Vn
 fy
where  = 1.4 for concrete placed monolithically,
 = 1.0 for concrete placed against hardened concrete (see ACI 11.7.4.3)
Step 3. Calculate required flexural reinforcement (11.9.3.3)
V a  N nc (h  d )
Af  n
f y ( jd )
(assume jd = 0.85)
Step 4. Reinforcement to carry tensile force (ACI 11.9.3.4)
An 
N nc
fy
Step 5. Required main flexural steel (As) is given by (ACI 11.9.3.5 and 11.9.5)

 2 Avf  An
 3
larger of  A f  An

f
0.04 c bd
fy

Step 6. Provide closed horizontal stirrups (ACI 11.9.4):
Ah = 0.5 (As – An)
Ensure adequate detailing (ACI 11.9.6 & 11.9.7)