Canadian Bolt Spacing and Edge Distance — CSA S16-19 Table 3 Requirements

Complete reference for bolt spacing and edge distance requirements per CSA S16-19 Table 3. Minimum and recommended distances for M16 through M36 bolts in Canadian structural steel connections, including sheared, rolled, and flame-cut edge conditions.

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CSA S16 Minimum Spacing Requirements

Per CSA S16-19 Table 3:

Bolt Diameter Min Centre-Centre Spacing Min Edge Distance (Sheared) Min Edge Distance (Rolled/Flame-Cut)
M16 3d = 48 mm (typically 60 mm) 27 mm 22 mm
M20 3d = 60 mm (typically 70 mm) 33 mm 27 mm
M22 3d = 66 mm (typically 70 mm) 36 mm 30 mm
M24 3d = 72 mm (typically 80 mm) 39 mm 32 mm
M27 3d = 81 mm (typically 90 mm) 45 mm 36 mm
M30 3d = 90 mm (typically 100 mm) 48 mm 39 mm
M36 3d = 108 mm (typically 120 mm) 57 mm 47 mm

Note: 3d = three times the nominal bolt diameter. The "typical" spacing values are CISC recommended practice and provide adequate clearance for tightening.

Standard Spacing Recommendations

Application Recommended Spacing Rationale
Minimum for any connection 3d (but not less than 60 mm for M20+) Code minimum — allows wrench clearance
Typical beam web connections 70-80 mm for M20 Standard bolt hole layout
Typical column splices 80-100 mm for M24 Allows for erection tolerance
Typical gusset plates 70-80 mm for M20 Standard layout
Tension connections 4d recommended Reduces stress concentration
Fatigue-critical connections 4-5d recommended Reduces net section stress
Oversized hole patterns 4d minimum Additional clearance

Edge Distance Requirements by Hole Type

Standard Holes (d_hole = bolt dia + 2 mm for d ≤ 24 mm, + 3 mm for d ≥ 27 mm)

Bolt Dia Standard Hole Dia Min Edge (Sheared) Min Edge (Rolled) Recommended Edge
M16 18 27 22 35
M20 22 33 27 40
M22 24 36 30 45
M24 26 39 32 50
M27 30 45 36 55
M30 33 48 39 60
M36 39 57 47 70

Oversized and Slotted Holes

Per CSA S16 Table 3, for oversize and slotted holes:

Bolt Dia Oversize Hole Dia Min Edge (Sheared) Min Edge (Rolled)
M16 20 32 27
M20 24 38 32
M22 26 41 35
M24 28 44 38
M27 32 50 44
M30 35 54 48
M36 42 64 54

Oversized holes require greater edge distances because of the larger hole diameter and reduced bearing area.

Minimum Edge Distance for Galvanised Connections

For hot-dip galvanised assemblies, the edge distance should be increased by:

Delta_e = 3 mm for M16-M20 Delta_e = 5 mm for M22-M30 Delta_e = 7 mm for M36

This accounts for the galvanising coating thickness (typically 85 microns per side minimum) and the risk of edge tearing due to the higher installation torques required for galvanised bolts (lower K factor).

Spacing for Wrench Clearance

The minimum centre-to-centre spacing must also consider the tightening tool:

Tool Type Clearance Required Effect on Spacing
Manual spud wrench 2d minimum Not governing
Impact wrench (standard socket) 3d minimum Typically governs
Impact wrench (thin-wall socket) 2.5d Reduces spacing
Torque wrench (calibrated) 3d minimum Typical
Hydraulic tensioner 4d minimum Special application
Hand tightening (DTI washers) 2.5d Check clearance

For most field bolting with impact wrenches, 3d centre-to-centre (70 mm for M20) is the practical minimum.

Worked Example — Bolt Layout for Gusset Plate

Given: 12 mm 350W gusset plate with 8-M20 A325M bolts in 2 rows of 4. Connection to HSS column face. Sheared edges.

Step 1 — Determine Minimum Distances: Edge distance (sheared, M20): 33 mm minimum → use 40 mm Bolt spacing (centre-centre): 60 mm minimum (3d) → use 70 mm

Step 2 — Layout Dimensions: Width of bolt group: 3 × 70 mm + 2 × 40 mm = 290 mm (for 4 bolts horizontally) Height between rows: 80 mm (recommended for M20) Distance between rows: 80 mm × 2 = 160 mm

Step 3 — Check Clearances: Edge distance along force direction: 40 mm End distance: 40 mm ≥ 33 mm. OK. Spacing: 70 mm ≥ 60 mm. OK.

Step 4 — Tearout Check at End Bolts: Br_tearout = phi_br × t × e × Fu = 0.80 × 12 × 40 × 450 / 1000 = 172.8 kN Vs per M20 = 75.0 kN per bolt (for 8 bolts with Cf = 600 kN: 75 kN each) 172.8 ≥ 75.0. OK.

Result: Layout: 290 mm wide × 160 mm high with 70 mm horizontal spacing, 40 mm edges, 80 mm row spacing. All clearances satisfied.

Special Requirements

Compression Connections

For compression members with bolted splices:

Tension Splices

For tension splices in primary members:

Seismic Connections

Per CSA S16 Clause 27.5, seismic connections have additional requirements:

Frequently Asked Questions

What is the minimum bolt spacing for M24 bolts per CSA S16? 3 × d = 3 × 24 = 72 mm minimum centre-to-centre spacing. The recommended practical spacing is 80 mm for M24 bolts. This accounts for both the code minimum and wrench clearance requirements. For connections where wrenches must access nuts in confined spaces, increase to 90-100 mm.

What is the minimum edge distance for M20 bolts on a sheared edge? 33 mm from the centre of the hole to the sheared edge per CSA S16 Table 3. This applies to the loaded and unloaded edges equally. Using 40 mm provides a reasonable margin for fabrication tolerance and increases tearout capacity. For rolled or flame-cut edges, the minimum is 27 mm.

Can bolt spacing be less than 3d in CSA S16? No. CSA S16-19 Table 3 explicitly requires 3d minimum centre-to-centre spacing for all bolt sizes. This minimum is based on: (a) preventing bearing failure interaction between adjacent holes, (b) providing sufficient net section, and (c) allowing tool clearance for installation. Spacing less than 3d requires rational testing per Clause 13.11.

What edge distance is required for oversized holes? For M20 in an oversized hole (24 mm diameter): 38 mm for sheared edges and 32 mm for rolled edges per CSA S16 Table 3. The larger edge distances for oversize holes account for the reduced bearing area and the possibility of the bolt bearing against the hole edge at a less favourable angle.

Related Pages

This page is for educational reference. Spacing and edge distance per CSA S16-19 Table 3. Verify against project-specific connection details. Oversized holes require RCSC approval for slip-critical connections. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

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