Bolt Pitch Distance — Minimum & Maximum, AISC J3.3 & Staggered Holes
Bolt pitch (p) is the longitudinal center-to-center spacing between adjacent bolt holes, measured parallel to the member's longitudinal axis. Together with gauge (transverse spacing) and edge distance, pitch defines the bolt hole layout grid. Correct pitch is essential for: (1) providing adequate net section between holes, (2) preventing tear-out and block shear failures, (3) ensuring wrench clearance during erection, and (4) sealing the faying surfaces against moisture.
Standard bolt spacing notation:
p = pitch (longitudinal spacing, parallel to member axis)
s = staggered pitch (diagonal distance between staggered holes)
g = gauge (transverse spacing, perpendicular to axis)
Le = edge distance (hole center to edge)
PRELIMINARY — NOT FOR CONSTRUCTION. All content is for educational and reference use only. Must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE) before use in any project.
Minimum Pitch — AISC J3.3
p_min = 2.67 × d (2-2/3 times nominal bolt diameter)
p_pref = 3.0 × d (preferred spacing for standard connections)
| Bolt Diameter (in) | p_min (in) | p_pref (in) | Hole Diameter (in) | Clear Distance (min) |
|---|---|---|---|---|
| 1/2 | 1.33 | 1.5 | 9/16 | 0.77 |
| 5/8 | 1.67 | 1.875 | 11/16 | 0.98 |
| 3/4 | 2.00 | 2.25 | 13/16 | 1.19 |
| 7/8 | 2.33 | 2.625 | 15/16 | 1.39 |
| 1.0 | 2.67 | 3.0 | 1-1/16 | 1.61 |
| 1-1/8 | 3.00 | 3.375 | 1-1/4 | 1.75 |
| 1-1/4 | 3.33 | 3.75 | 1-3/8 | 1.96 |
The clear distance between holes is p_min − d_hole = 0.48d for the minimum pitch. The 2.67d minimum ensures that the net section between adjacent holes has adequate tensile and bearing strength, and that tear-out between holes does not govern over bolt shear.
Maximum Pitch — AISC J3.5
Maximum pitch limits prevent plate separation due to buckling and moisture ingress:
| Condition | p_max |
|---|---|
| Painted members or unpainted not subject to corrosion | 24 × t (thinner plate) ≤ 12 in |
| Unpainted weathering steel subject to corrosion | 14 × t (thinner plate) ≤ 7 in |
Where t is the thickness of the thinner connected plate. These limits ensure the plates remain in contact and prevent local buckling of the unconnected length between bolts.
Example — 3/8 in connection plate, painted: p_max = 24 × 0.375 = 9.0 in ≤ 12 in → maximum pitch = 9.0 in
Staggered Pitch and Net Section — The s²/4g Rule
When bolts are staggered (offset in alternating rows), the net section path is not a straight transverse line. The failure path follows a zigzag, and the effective width reduction is:
b_net = b_gross − Σ(d_hole) + Σ(s² / 4g) (AISC B4.3b)
Where s is the longitudinal stagger (pitch component along the diagonal between staggered holes) and g is the transverse gauge.
Worked example — Staggered net section:
A 12-in wide tension plate (t = 1/2 in) has staggered 3/4 in bolt holes. Gauge g = 3.0 in, staggered pitch s = 2.5 in. Three holes in a zigzag path.
Path 1 (straight across — 2 holes):
b_net1 = 12.0 − 2 × (13/16 + 1/16) = 12.0 − 2 × 0.875 = 10.25 in
(Deduct hole diameter = 13/16 in for 3/4 in bolt + 1/16 in for damage = 7/8 in)
Path 2 (zigzag — passes through 3 holes):
b_net2 = 12.0 − 3 × 0.875 + 2 × (2.5² / (4 × 3.0))
= 12.0 − 2.625 + 2 × (6.25 / 12.0)
= 12.0 − 2.625 + 2 × 0.521
= 12.0 − 2.625 + 1.042 = 10.42 in
Although Path 2 passes through 3 holes (larger deduction), the s²/4g additions partially offset the extra hole. The critical path is the straight-across Path 1: b_net = 10.25 in governs.
Practical Connection Layout Guidelines
| Design Rule | Value | Source |
|---|---|---|
| Minimum pitch | 2.67d | AISC J3.3 |
| Preferred pitch | 3d | Industry std |
| Maximum pitch (painted) | min(24t, 12 in) | AISC J3.5 |
| Minimum edge distance (sheared edge) | 1.25d to 1.75d | AISC Table J3.4 |
| Minimum edge distance (rolled edge) | 0.75d to 1.25d | AISC Table J3.4 |
| Wrench clearance (socket) | ~1.5d from adjacent | OSHA/fabricator |
For standard beam-to-column shear connections (double-angle, shear tab), a pitch of 3 in is typical for 3/4 in bolts — slightly above the preferred 2.25 in to provide generous wrench clearance and simplify erection.
Frequently Asked Questions
What is the difference between pitch and gauge?
Pitch is longitudinal (along member axis) center-to-center spacing. Gauge is transverse (across member width) center-to-center spacing. Pitch is denoted p; gauge is denoted g. In staggered patterns, the diagonal distance s = sqrt(p² + g²) is used in the s²/4g rule.
Can pitch be less than 2.67d?
Only with explicit justification and engineering judgment. The 2.67d minimum is a code-prescribed limit intended to prevent tear-out between holes. For very thin plates or special connection geometries, larger pitch may be required by bearing/tear-out calculations even if 2.67d is met.
Why does maximum pitch depend on whether the steel is painted?
Unpainted members allow moisture to penetrate between plies, accelerating corrosion. The tighter maximum pitch (14t vs 24t) ensures more bolts hold the plates together, minimizing gaps where moisture can collect. Weathering steel (unpainted) is particularly affected because its protective patina requires wet-dry cycling — trapped moisture prevents proper patina formation.
Related Terms and Pages
- Bolt Gauge Distance — g1/g2/g3 & Standard Gauges
- Staggered Bolt Pattern — Net Section & s²/4g Rule
- Block Shear — Definition & Failure Mode
- Prying Action — Definition & Bolt Force
- Bearing-Type Connection — Definition & AISC J3
- Bolted Connection Calculator — Free Online Tool
Educational reference only. Bolt pitch, gauge, and edge distance must comply with AISC 360 Section J3. All designs must be independently verified by a licensed Professional Engineer. Connection geometry also affects erection safety and must consider ironworker access.
Disclaimer: This content is for educational purposes only. Results must be verified by a licensed professional engineer. Steel Calculator provides preliminary design tools — NOT a substitute for professional engineering judgment.