Column tie spacing requirements per ACI 318-19
Ties in a tied column restrain the longitudinal bars against buckling and confine the core. ACI 318-19 sets three families of rules: a maximum tie spacing (§25.7.2.1), a minimum tie size (§25.7.2.2), and bar-arrangement rules (§25.7.2.3). This page covers all three; calcnote's engine automatically checks the first two on every input.
Maximum spacing — the §25.7.2.1 envelope
Tie spacing along the column may not exceed the least of four limits:
- 16 longitudinal-bar diameters — restrains the vertical bars against buckling between ties.
- 48 tie-bar diameters — keeps the tie itself effective (a thin tie spaced far apart does little).
- The least section dimension (b or h) — a floor on confinement of the concrete core.
Lookup table — governing maxima by bar size
| Longitudinal bar | db (in) | 16·db (in) | Max with #3 ties (in) | Max with #4 ties (in) |
|---|---|---|---|---|
| #6 | 0.750 | 12.0 | 12.0 | 12.0 |
| #7 | 0.875 | 14.0 | 14.0 | 14.0 |
| #8 | 1.000 | 16.0 | 16.0 | 16.0 |
| #9 | 1.128 | 18.05 | 18.0* | 18.05 |
| #10 | 1.270 | 20.32 | 18.0* | 20.32 |
| #11 | 1.410 | 22.56 | not permitted (§25.7.2.2) | 22.56 |
48·dtie = 18.0 in for #3 ties, 24.0 in for #4 ties. The final limit is also capped by the least section dimension — a 12×20 column caps everything above at 12 in regardless of bars.
* Near-miss worth noticing: for #9 bars with #3 ties, 48·dtie = 18.00 in governs over 16·db = 18.05 in by five-hundredths of an inch — and for #10 bars with #3 ties the tie limit governs outright. Upsizing to #4 ties recovers the bar-based limit.
You don't need to carry this table to every check — calcnote validates §25.7.2.1 and §25.7.2.2 on every input and rejects violations with the governing limit named. See a live sample result — no signup.
Minimum tie size — §25.7.2.2
#3 ties are permitted for longitudinal bars up to #10. #11 and larger longitudinal bars (and bundled bars) require at least #4 ties. That is why the #11/#3 cell above is struck — the combination is not a spacing problem but a tie-size violation.
Arrangement rules — §25.7.2.3
Spacing and size are necessary but not sufficient — rectilinear ties must also be arranged so that:
- Every corner bar and every alternate longitudinal bar has lateral support from the corner of a tie with an included angle of no more than 135°.
- No unsupported bar sits farther than 6 in clear along the tie from a laterally supported bar.
End-region placement rules (for example, locating the first tie within half a tie spacing above the top of a footing or slab) appear in §10.7.6.2. Scope note: calcnote checks the spacing envelope and minimum tie size; tie arrangement and end-region placement remain the designer's responsibility. Columns in special seismic systems follow the stricter hoop provisions of §18.7.5, which are outside calcnote's scope.
Sources
- ACI 318-19: §25.7.2.1 (spacing), §25.7.2.2 (minimum tie size), §25.7.2.3 (arrangement), §10.7.6.2 (end-region placement), §18.7.5 (seismic hoops, out of scope).