Compute ACI 318-19 two-way shear vs for single- or multiple-leg stirrups per 22.6.7.2. Checks 22.6.7.1 applicability instantly. Try it free on CalcTree.
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About this Two-Way Shear Stirrups (vs) Calculator
This calculator computes the two-way shear stress strength provided by slab/footing stirrups, v_s, using ACI 318-19 Clause 22.6.7.2. It also checks the visible applicability requirements from 22.6.7.1 (including minimum effective depth and bar-diameter ratio) and forces a manual confirmation input for any 22.6.7.1 requirements not visible in the source screenshot/page capture.
- Structural engineer — quantify how much two-way shear demand is carried by stirrups (v_s) and confirm the section qualifies to use the stirrup provision before relying on the result.
- Detailer / reinforcement designer — iterate leg count/area and spacing inputs and see the direct impact on v_s while keeping the ACI 22.6.7.1 applicability checks in view.
- Checker / reviewer — audit that the use of slab/footing stirrups is permitted (including the manual confirmation for unseen clause items) and confirm the computation aligns with the code equation.
This is an engineering-grade calculator on CalcTree: inputs, intermediate ratios, and applicability flags are exposed so the result can be checked, reviewed, and reused across projects.
More info on Two-Way Shear Stirrups (vs)
Inputs
The calculator takes the geometric and reinforcement parameters used directly by ACI 318-19 22.6.7.2: the total stirrup-leg area on one peripheral line A_v, stirrup yield strength f_yt, critical section perimeter b_o (from 22.6.4), and the spacing of peripheral lines s. It also requires effective depth d and stirrup bar diameter d_b to evaluate the visible 22.6.7.1 applicability limits tied to member geometry and reinforcement scale.
Applicability checks from ACI 318-19 22.6.7.1
Before using 22.6.7.2, the page checks the visible 22.6.7.1 conditions shown in the source material, including a minimum effective depth requirement and a minimum ratio of effective depth to stirrup diameter (implemented as d and d_b checks). Because not all of 22.6.7.1 may be visible in the referenced screenshot/page capture, the calculator includes a required “other conditions” confirmation input sourced from the separate 22.6.7.1/page to ensure the user explicitly confirms the remainder of the clause requirements have been satisfied.
Shear stress contribution from stirrups (ACI 318-19 22.6.7.2)
The calculator computes the stirrup-provided two-way shear stress as:
v_s = (A_v f_yt) / (b_o s)
A_v is taken as the sum of all stirrup legs on one peripheral line that is geometrically similar to the column perimeter, and s is the spacing between successive peripheral lines measured perpendicular to the column face. The implementation is a direct application of the clause equation, using the same b_o perimeter basis used for two-way shear checks.
Outputs and reporting
The page reports the computed ratio d/d_b alongside the minimum required value used for the 22.6.7.1 diameter-ratio check, the final v_s value, an applicability note explaining whether 22.6.7.1 is fully satisfied/confirmed, and a single overall traffic-light result summarizing the applicability status. A separate positive-inputs sanity check flags non-physical or invalid inputs before the code checks are relied upon.
Common Calculation Errors to Avoid
- Using v_s without satisfying 22.6.7.1 — the 22.6.7.2 equation is only valid when the clause applicability requirements are met; failing the member-type/depth/ratio checks invalidates the result.
- Forgetting the “other conditions” confirmation — if the full clause text is not visible in your reference, you still need to confirm the remaining 22.6.7.1 requirements from the source document before using v_s.
- Wrong A_v definition — A_v must be the sum of areas of all legs on one peripheral line geometrically similar to the column perimeter; mixing legs from multiple lines or counting only one leg will skew v_s.
- Inconsistent b_o perimeter basis — b_o must match the critical section definition from 22.6.4 used for your punching shear evaluation; using a different perimeter than the one used for v_u comparisons breaks consistency.
- Spacing direction error for s — s is the spacing of peripheral lines measured perpendicular to the column face; using a tangential spacing or a different direction will misstate v_s.
- Unit inconsistency — ensure A_v, f_yt, b_o, and s are entered with compatible units so v_s is returned in the correct stress units.
- Ignoring basic input sanity — non-positive d, d_b, b_o, or s (or unrealistic reinforcement properties) can produce meaningless outputs even if the equation evaluates numerically.
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FAQs
What does ACI 318-19 Clause 22.6.7.2 actually compute?
Clause 22.6.7.2 gives the two-way shear stress contribution from single- or multiple-leg stirrups at a critical section around a column. The formula is vs = Av · fyt / (bo · s), where Av is the total leg area on one peripheral line, bo is the critical perimeter from 22.6.4, and s is the spacing between peripheral lines perpendicular to the column face. This vs value feeds into the overall punching shear strength check for the slab or footing.
What are the applicability requirements from ACI 318-19 Clause 22.6.7.1?
Before using 22.6.7.2, the member must be a slab or footing, the effective depth d must be at least 6 in., and d must be at least 16 times the stirrup bar diameter db. All three conditions must pass for stirrups to be a permitted shear reinforcement type under this clause. The template checks the two geometric conditions directly from your inputs and asks you to manually confirm the member type.
Why does the template include a confirmation input for additional 22.6.7.1 conditions?
The full text of 22.6.7.1 may contain requirements beyond what is visible in the code screenshot embedded in this page. Rather than silently ignore those provisions, the template includes a required Yes/No confirmation asking you to verify those conditions independently against your copy of ACI 318-19. The overall applicability check will fail until you set that input to Yes.
How is Av defined for a peripheral line of stirrups?
Av is the sum of the cross-sectional area of all stirrup legs that fall on a single peripheral line geometrically similar to the column perimeter. If you have multiple legs per stirrup unit arranged around the column at the same radial distance, add all their areas together. Do not mix legs from different peripheral lines; each line is evaluated separately, and s is the distance between adjacent peripheral lines.
What inputs do I need to run this calculation?
You need the effective depth d, stirrup bar diameter db, total stirrup leg area on one peripheral line Av, yield strength of the shear reinforcement fyt, critical section perimeter bo from 22.6.4, and stirrup spacing s. You also need to confirm via the radio inputs that the member is a slab or footing and that any additional 22.6.7.1 conditions not visible on this page are satisfied.
What should I do if the d ≥ 16db check fails?
A failing d ≥ 16db check means your stirrup bar is too large relative to the slab thickness for ACI 318-19 to permit stirrups as the shear reinforcement type under 22.6.7. You have two practical options: use a smaller diameter stirrup bar so the ratio is met, or switch to a different shear reinforcement system such as headed studs covered under 22.6.8. Do not use the vs result from 22.6.7.2 if this applicability check fails.
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