ACI 318-19: Maximum Spacing of Shear Reinforcement - Columns (Table 10.7.6.5.2)

About this ACI 318-19: Maximum Spacing of Shear Reinforcement - Columns (Table 10.7.6.5.2) Calculator

This calculator checks the maximum allowable spacing of shear reinforcement in concrete columns per ACI 318-19 Table 10.7.6.5.2. It evaluates the factored shear demand against a threshold based on concrete strength and section geometry, then returns the governing spacing limit for either nonprestressed or prestressed columns.

• Structural engineer — verify tie, hoop, or spiral spacing against code limits during column design, with the threshold check and governing spacing computed automatically for both low- and high-shear conditions.
• Reinforced concrete designer — quickly confirm compliance when iterating on column geometry or shear reinforcement layout, without manually working through both branches of Table 10.7.6.5.2.
• Plan checker or reviewer — audit submitted column designs against ACI 318-19 spacing requirements with a transparent, traceable calculation that shows every intermediate value.

This is an engineering-grade calculator built on CalcTree, where calculations are live, auditable, and can be saved directly to a project workspace.

More info on ACI 318-19: Maximum Spacing of Shear Reinforcement - Columns (Table 10.7.6.5.2)

Inputs

The calculator requires six inputs covering the column type, section geometry, material strength, shear demand, and the provided reinforcement spacing. Column type is selected as either nonprestressed or prestressed, which determines which branch of Table 10.7.6.5.2 applies. Section geometry inputs include the effective depth, overall section depth, and web width. The specified compressive strength of concrete feeds the threshold calculation. Factored shear at the section of interest and the provided spacing of ties, hoops, or spiral reinforcement complete the input set.

Threshold Calculation

Before a spacing limit can be selected, the calculator evaluates the threshold quantity defined in Table 10.7.6.5.2. This threshold is a function of the square root of the specified concrete compressive strength, the web width, and the effective depth. The factored shear demand is compared against this threshold to determine which row of the table governs. When the factored shear exceeds the threshold, the code requires tighter spacing limits, reflecting the increased demand on shear reinforcement in higher-shear conditions.

Maximum Spacing Limits

Once the governing table row is identified, the calculator applies the appropriate spacing limit based on column type. For nonprestressed columns, the limit is expressed in terms of the effective depth, capped at an absolute maximum in inches. For prestressed columns, the limit is expressed as a fraction of the overall section depth, again capped at an absolute maximum. In both cases, the code imposes stricter limits when factored shear exceeds the threshold, halving the fraction of depth used to compute the limit. The calculator evaluates all relevant expressions and returns the single governing maximum spacing.

Design Check and Output

The summary table presents the threshold force, the governing maximum spacing, and the provided spacing, alongside a pass/fail result. The spacing check confirms whether the provided tie, hoop, or spiral spacing satisfies the ACI 318-19 requirement. A pass result means the provided spacing is at or below the computed maximum; a fail flags a non-compliant condition that requires the designer to reduce the spacing before finalising the column design.

Common Calculation Errors to Avoid

• Using total section depth instead of effective depth for nonprestressed columns — the nonprestressed spacing limits are based on the effective depth to the tension reinforcement, not the overall section depth; confusing the two produces unconservative results.
• Applying the wrong column type branch — prestressed and nonprestressed columns use different geometric expressions for the spacing limit, so selecting the wrong type changes the outcome even when all other inputs are identical.
• Taking the square root of a value with inconsistent units — the empirical term involving the square root of concrete compressive strength requires the strength to be expressed in psi before taking the root; using ksi without appropriate conversion will produce a threshold that is off by a factor of approximately 31.6.
• Ignoring the absolute cap on spacing — both branches of Table 10.7.6.5.2 impose hard upper limits in inches regardless of section size; large sections where the depth-based expression exceeds the cap must use the capped value.
• Checking spacing at only one location — factored shear varies along the column height, and the threshold comparison should be made at the critical section where demand is highest; a spacing that passes at mid-height may fail near a joint or connection.
• Confusing provided spacing with centre-to-centre spacing — the code limit applies to the centre-to-centre spacing of transverse reinforcement sets, not the clear gap between them.

FAQs

What does ACI 318-19 Table 10.7.6.5.2 govern and why does it matter?

Table 10.7.6.5.2 sets the maximum allowable spacing of shear reinforcement (ties, hoops, or spirals) in columns. Tighter spacing limits apply when shear demand is high, because closely spaced transverse reinforcement provides better diagonal crack control, confinement, and ductility. Exceeding the maximum spacing is a code violation regardless of whether shear capacity calculations pass.

What is the threshold shear that triggers tighter spacing limits?

The threshold is 4√f'c · bw · d, where f'c is in psi. If the factored shear Vu at the section exceeds this value, the maximum spacing drops from d/2 to d/4 for nonprestressed columns (capped at 12 in instead of 24 in). The calculation computes this threshold automatically based on your inputs so you can see directly which row of the table governs.

How do the spacing limits differ between nonprestressed and prestressed columns?

For nonprestressed columns, limits are based on effective depth d: either d/2 or d/4 depending on shear demand. For prestressed columns, limits reference overall section depth h instead: either 3h/4 or 3h/8. Both cases share the same absolute caps of 24 in (low shear) and 12 in (high shear). Select the correct column type in the dropdown to ensure the right limits are applied.

What inputs do I need to run this calculation?

You need the factored shear at the section Vu, section width bw, effective depth d, overall section depth h, specified concrete compressive strength f'c, and the provided tie or hoop spacing s_prov. For nonprestressed columns, h is not used in the spacing formula but is still required if you switch to prestressed. Enter all values and the page resolves the governing limit automatically.

Can this calculation be used for both tied columns and spiral columns?

Yes. The ACI 318-19 Table 10.7.6.5.2 limits apply to shear reinforcement in general, whether ties, hoops, or spirals. The spacing check compares your provided spacing against the governing maximum regardless of reinforcement type. Just make sure the value you enter for s_prov reflects the actual pitch or spacing used in your design.

My spacing passes the shear check but the column still needs confinement ties — does this cover that?

No. This calculation only checks maximum spacing for shear per Table 10.7.6.5.2. Confinement requirements in seismic or special moment frame regions are governed by separate provisions, including ACI 318-19 Section 18.7.5 for special structural walls and columns. Always check confinement limits independently, as they often control over shear spacing in practice.