Beam shear reinforcement calculator
Select ACI 318-19 or ACI 318-19(22). The calculator selects the concrete shear equation from the provided Av compared with Av,min, computes the longitudinal reinforcement ratio and axial-force contribution, and checks strength, minimum stirrup demand and the applicable spacing limit.
| Term | Value |
|---|---|
| Effective depth d | 440 mm |
| Tension reinforcement As | 1257 mm² (4 × 20 mm bars) |
| Longitudinal ratio ρw | 0.0095 |
| Axial term Nu/(6Ag) | 0.00 MPa (compression capped at 0.05f′c) |
| ACI edition | ACI 318-19 |
| Stirrup area Av | 157 mm² |
| Minimum stirrup area Av,min | 50 mm² |
| Minimum shear demand threshold | 43.5 kN |
| Minimum area required by demand | Required and met |
| Vc equation branch | ACI 318-19 / 318-19(22) Eq. (a), Av ≥ Av,min |
| Vc | 118.7 kN |
| Vs | 145.1 kN |
| φVn | 197.9 kN |
| Nominal strength limit | 461.0 kN |
| Maximum stirrup spacing | 220 mm |
| Shear stress vu/(bw·d) | 1.14 MPa |
The Av,min branch is applied even when minimum stirrups are not required by demand. Exceptions for shallow beams, slab-integral beams, steel-fiber beams and joists are not evaluated.
Vc = (0.17 λ √f′c + Nu/(6Ag)) bw d · ACI 318-19 and 318-19(22) Table 22.5.5.1; branch selected from Av versus Av,min.
Vs = Av fy d / s · Vertical stirrups, 45° cracking assumed.
Nu/(6Ag) ≤ 0.05f′c · Compression positive; tension negative.
Av,min = max(0.062√f′c, 0.35) bw s / fy · ACI 318-19 §9.6.3.4, SI units.
Provide Av,min where Vu > 0.083 φ λ √f′c bw d · ACI 318-19 §9.6.3.1 in SI units; Table 9.6.3.1 exceptions are not evaluated.
φVn = φ min(Vc + Vs, Vn,max) ≥ Vu · Checks shear strength, nominal maximum, minimum reinforcement trigger and spacing.
A clear path from inputs to results.
Select ACI 318-19 or 318-19(22), reapproved 2022. The calculator selects Vc from Av versus Av,min, uses the size-effect and longitudinal-steel ratio branch when Av is below minimum, includes the axial-force term, and checks strength, minimum reinforcement and stirrup spacing.
How to use
- Choose ACI 318-19 or 318-19(22), then enter web width, depth, clear cover to the stirrup outside, and tension-bar size/count.
- Set f′c, stirrup fy and factored axial load Nu (compression positive).
- Choose the number of legs, stirrup diameter and spacing.
- Enter the factored shear.
The formula
Reference: ACI 318-19 / 318-19(22) Table 22.5.5.1 and §§22.5.5, 22.5.10, 9.6.3 and 9.7.6; λs per Table 22.5.5.1.3.
Worked example
300 × 500 mm, four 20 mm tension bars, 2-leg 10 mm at 200 mm, Vu 150 kN
- bw 300 mm, h 500 mm, clear cover to stirrup outside 40 mm, 20 mm main bars.
- Four tension bars in one layer; no axial force; ACI 318-19.
- f′c 28 MPa, stirrup fy 420 MPa.
- 2 legs of 10 mm at 200 mm.
- Vu 150 kN.
- 1
d = 500 − 40 cover − 10 stirrup − 10 = 440 mm.
- 2
As = 4 × π × 20²/4 = 1,257 mm²; ρw = As/(bw·d) = 0.0095.
- 3
Av = 157 mm².
- 4
Av,min = max(0.062√28, 0.35) × 300 × 200 / 420 = 50 mm²; Av ≥ Av,min, so use Eq. (a).
- 5
Vc = (0.17 × √28) × 300 × 440 = 118.7 kN.
- 6
Vs = 157 × 420 × 440 / 200 = 145.1 kN.
- 7
φVn = 0.75 × 263.8 = 197.9 kN; utilisation 75.8%.
- 8
Vu > 0.083φλ√f′c bw d, so minimum stirrups are required. Spacing limit d/2 = 220 mm, so 200 mm is acceptable.
φVn 197.9 kN · utilisation 75.8% · spacing OK.
Interpreting the result
Shear failures are brittle. For this ACI 318-19 / 318-19(22) model, the selected concrete equation depends on Av relative to Av,min; minimum stirrups are also checked against the demand trigger. If utilisation is close to 1.0, add reinforcement only after checking the section maximum and detailing limits.
Assumptions & limitations
- Vertical stirrups only.
- Normal-weight concrete (λ = 1.0).
- Rectangular, nonprestressed beam with one layer of tension steel; As is estimated from the entered bar count and diameter.
- Effective depth is measured to the tension-bar centroid using clear cover to the outside of the stirrup; bar fit and clear spacing are not checked.
- Axial force is uniform and compression is positive; Nu/(6Ag) is capped at 0.05f′c.
- Torsion, prestress, shear demand along the span, strain compatibility and seismic detailing are not checked. Exceptions to minimum shear reinforcement are not evaluated.
- ACI 318-25 updates one-way shear provisions and is not implemented; only 318-19 and 318-19(22) are offered.
Frequently asked questions
Why is nominal shear strength capped?
ACI limits the combined nominal shear strength to prevent diagonal-compression failure of the web.
Does this apply to slabs?
No. Slabs and footings use different provisions.
When is minimum shear reinforcement required?
The model checks the ACI 318-19 §9.6.3.1 SI trigger Vu > 0.083φλ√f′c bw d, then compares the provided Av with Av,min. ACI requires the size-effect equation (c) when Av is below Av,min even if demand does not trigger minimum stirrups.
Methodology last reviewed 2026-10-21. Results are informational and not financial or engineering advice — see our disclaimer.