RC Beam Shear Check Calculator
Estimate the shear capacity of a reinforced-concrete beam using a simplified AS 3600 approach. The tool returns the concrete contribution Vc, the stirrup (shear reinforcement) contribution Vs and the combined design capacity φVn. Add your applied design shear V* to get the shear utilisation and an OK / over-capacity flag.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the beam width b (mm) and the effective depth d (mm). Optionally override the concrete strength f'c (default 32 MPa) and the shear capacity factor φ (default 0.7).
- To include shear reinforcement, enter the stirrup area per set Asv (mm² — the total area of the legs crossing the crack), the stirrup spacing s (mm) and, if not 500 MPa, the stirrup yield fsy. Leave Asv and s blank for the concrete-only capacity.
- Optionally enter the applied design shear V* (kN) to see the utilisation as a percentage of φVn.
How it works
The concrete contribution is Vc = 0.17·√f'c·b·d, converted from newtons to kN by dividing by 1000. Vertical stirrups add Vs = Asv·fsy·d / s, which is the steel force per set times the number of sets crossing a 45° crack (d/s). The design capacity is φVn = φ·(Vc + Vs) with φ ≈ 0.7 for shear. Utilisation = V* / φVn × 100.
Worked example
Worked example. b = 300 mm, d = 450 mm, f'c = 32 MPa. Vc = 0.17×√32×300×450 / 1000 = 129.825 kN. Concrete-only φVn = 0.7×129.825 = 90.877 kN. Adding Asv = 157 mm², fsy = 500 MPa, s = 200 mm gives Vs = 157×500×450 / 200 / 1000 = 176.625 kN and φVn = 0.7×(129.825 + 176.625) = 214.515 kN.
Common mistakes
- Entering only one of Asv or s. Both the stirrup area and the spacing are needed to compute Vs; if either is blank the tool reports the concrete-only capacity.
- Using Asv for a single leg. Asv is the total cross-sectional area of all stirrup legs that cross the shear plane at one location (e.g. two legs of a closed tie).
- Treating φVn as the final design shear. This simplified form omits the web-crushing upper limit (Vu,max), the minimum-shear-reinforcement rule and the AS 3600 angle factors, so a detailed check is still required.
Frequently asked questions
Why is the concrete term 0.17·√f'c?
It is a widely used lower-bound estimate of the shear stress a cracked concrete section can carry, expressed in MPa when f'c is in MPa. Multiplying by the shear area b·d gives a force in newtons. The full AS 3600 method modifies this with size, axial-load and reinforcement factors.
Does spacing s have an upper limit?
Yes. Codes cap the maximum stirrup spacing (commonly around 0.5d–0.75d and an absolute limit) so a diagonal crack is always crossed by at least one stirrup. This tool does not enforce that limit — check it separately.
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