ACI 318-19 Section 9.6 | Minimum Flexural Reinforcement
To prevent sudden, brittle failure upon cracking, concrete beams must contain a minimum amount of flexural reinforcement. If the beam's moment capacity is relied upon, it must be stronger than the cracking moment of the concrete section.
Governing Formula
Variables
Quick Example
Determine properties
Given a 12" wide, 24" deep beam with d = 21.5", f'c = 4000 psi, fy = 60000 psi.
Calculate limits
Calculate both minimum reinforcement equation limits.
Select maximum
The minimum area of steel required is the larger of the two values computation.
When does this govern?
This check typically governs for deep, lightly loaded beams, such as grade beams or basement walls where the required strength is very small but the section is large.
Common Mistake
Applying the minimum reinforcement requirement to a T-beam where the flange is in tension. In this case, the web width (bw) is replaced by the smaller of 2 times the web width or the flange width.