Minimum Flexural Reinforcement As,min (ACI 318-19 9.6.1.2)
The least flexural steel a concrete beam is allowed to have.
Example
You enter
- Concrete strength f'c (psi) 4000
- Steel yield fy (psi) 60000
- Web width bw (in) 12
- Effective depth d (in) 20
You get
- Minimum area As,min 0.80 in^2
Checked against published worked examples from: StructurePoint.
Details, formula, and sources
ScopeAs,min = max(3 sqrt(f'c)/fy, 200/fy) x bw x d, so the beam does not fail suddenly at first cracking. 4000 psi, Grade 60, 12x20 -> 0.80 in^2 (200/fy floor governs); at 5000 psi the sqrt term governs, 0.85 in^2. A design aid; the engineer of record's stamped design governs.
Formula or tableratio = max(3 sqrt(f'c)/fy, 200/fy); As,min = ratio x bw x d.
Source and editionThe ACI 318-19 9.6.1.2 minimum flexural reinforcement, by name.
Free accessACI 318 is readable free through the ACI online reading room at concrete.org; the 9.6.1.2 minimum-reinforcement provisions are in the published code.
What governsEstimate. AHJ and licensed professional govern.
API field namesfc_psi, fy_psi, bw_in, d_in, as_min_in2
- Minimum steel As,min = max(3 sqrt(f'c)/fy, 200/fy) x bw x dACI 318-19 9.6.1.2
- Floor crossover 200/fy governs to ~4444 psi; 3 sqrt(f'c)/fy aboveACI 318-19
- Rectangular web flange-in-tension bw substitution not applied herescope of this tile