UK Bolt Spacing and Edge Distance — EN 1993-1-8 Table 3.3 + UK NA
Minimum and maximum bolt spacing, edge distance, and end distance requirements per EN 1993-1-8 Table 3.3 with UK National Annex modifications. Covers standard UK detailing practice for M12 to M36 bolts in structural steel connections, referencing BS EN 1090-2 execution classes and SCI guidance for UK steelwork contractors.
Quick access: UK Steel Grades | UK Steel Properties | UK Beam Sizes | UK Bolt Capacity | All UK References
EN 1993-1-8 Table 3.3 — Spacing Requirements
| Parameter | Symbol | Minimum | Maximum | Notes |
|---|---|---|---|---|
| End distance | e1 | 1.2d0 | 4t + 40 mm | Measured from bolt hole centre to plate end |
| Edge distance | e2 | 1.2d0 | 4t + 40 mm | Measured from bolt hole centre to plate edge |
| Bolt pitch (in direction of load) | p1 | 2.2d0 | 14t (comp) / 28t (tension) | Min: 14t for compression flange |
| Gauge (perpendicular to load) | p2 | 2.4d0 | 14t (comp) / 28t (tension) | Min: for tension members in open sections |
| Staggered pitch | — | 1.4d0 | — | For staggered bolt rows |
| Distance in staggered row | — | 2.4d0 | — | Between staggered and straight rows |
Where d0 = hole diameter, t = thinner connected plate thickness.
Standard UK Spacing Values (M12-M36)
| Bolt | d0 (mm) | Min e1/e2 | Standard e1 | Standard e2 | Min p1 | Standard p1 | Min p2 | Standard p2 |
|---|---|---|---|---|---|---|---|---|
| M12 | 14 | 17 | 30 | 25 | 31 | 60 | 34 | 55 |
| M16 | 18 | 22 | 35 | 30 | 40 | 70 | 44 | 60 |
| M20 | 22 | 27 | 40 | 30 | 49 | 70 | 53 | 60 |
| M22 | 24 | 29 | 45 | 35 | 53 | 80 | 58 | 65 |
| M24 | 26 | 32 | 50 | 40 | 58 | 80 | 63 | 70 |
| M27 | 30 | 36 | 55 | 45 | 66 | 90 | 72 | 80 |
| M30 | 33 | 40 | 60 | 45 | 73 | 100 | 80 | 85 |
| M36 | 39 | 47 | 70 | 55 | 86 | 120 | 94 | 100 |
Standard values reflect typical UK practice per SCI P358 (Joint Design for Steel Structures) and BS EN 1090-2.
Maximum Spacing Rules
| Condition | Maximum | Reason |
|---|---|---|
| Compression flange (exposed) | 14 × t_min | Prevent local buckling between bolts |
| Compression flange (painted) | 14 × t_min | Same — painting does not provide restraint |
| Tension flange (painted) | 28 × t_min | Adequate for corrosion protection access |
| Tension flange (exposed + weather) | 14 × t_min | Weathering steel requires tighter spacing |
| Any member in corrosive environment | 14 × t_min | EN 1090-2 Table 11 requirement |
Hole Sizes per BS EN 1090-2
| Bolt Size | Standard Round (d0) | Oversize (d0) | Short Slot | Long Slot |
|---|---|---|---|---|
| M12 | 14 | 16 | 14×18 | 14×30 |
| M16 | 18 | 20 | 18×22 | 18×40 |
| M20 | 22 | 24 | 22×26 | 22×50 |
| M24 | 26 | 30 | 26×30 | 26×60 |
| M27 | 30 | 34 | 30×35 | 30×68 |
| M30 | 33 | 37 | 33×38 | 33×76 |
UK NA Modifications
The UK NA to BS EN 1993-1-8 does not modify Table 3.3 minimum or maximum spacing requirements. The UK NA confirms:
- Minimum edge distance: 1.2d0
- Minimum pitch: 2.2d0
- Minimum gauge: 2.4d0
- These values apply to both building and bridge structures
The UK NA emphasises that for slotted holes, the minimum edge distance should be measured from the end of the slot, not the centre of the hole. For oversized holes, the edge distance is measured from the edge of the oversized hole.
Design Resources
- UK Steel Grades Reference — EN 10025-2 grade selection for UK projects
- UK Steel Mechanical Properties — fy, fu, and elongation tables
- UK Universal Beam and Column Sizes — UB/UC section dimensions and properties
- UK Bolt Capacity Tables — Class 8.8 and 10.9 bolt resistance
- UK Beam Design Guide — EN 1993-1-1 flexure, shear, and LTB
- UK Connection Design Guide — EN 1993-1-8 bolted and welded joints
- All UK Steel Design References — complete library
Frequently Asked Questions
What is the minimum edge distance for an M20 bolt in UK steelwork?
The minimum edge distance is e1 = e2 = 1.2 × d0 = 1.2 × 22 = 26.4 mm per EN 1993-1-8 Table 3.3. UK standard practice uses 40 mm for e1 (end distance) and 30 mm for e2 (edge distance) to provide adequate bearing resistance and accommodate standard fabrication tolerances per BS EN 1090-2. The larger values allow for hole positioning tolerances of ±2 mm.
What is the difference between pitch p1 and gauge p2?
Pitch p1 is the centre-to-centre distance between bolts in the direction of load transfer (parallel to the member axis). Gauge p2 is the centre-to-centre distance perpendicular to the load direction. Minimum p1 = 2.2d0 (governed by tear-out resistance and installation clearance). Minimum p2 = 2.4d0 (governed by plate bearing interaction and nut tightening clearance). Standard UK values for M20: p1 = 70 mm, p2 = 60 mm.
What are the maximum bolt spacing limits per BS EN 1090-2?
Maximum spacing depends on the condition of the connected parts. For compression elements: 14 × t_min (thinnest connected plate). For tension elements: 28 × t_min in standard environments, 14 × t_min in corrosive environments. Additionally, maximum edge distance from any bolt to the nearest plate edge is 4t + 40 mm ≤ 100 mm (if exposed) or 150 mm (if enclosed). These limits ensure adequate sealing against corrosion and prevent local buckling between fasteners.
Does the UK NA modify Table 3.3 spacing requirements?
No. The UK NA to BS EN 1993-1-8 adopts Table 3.3 spacing, edge distance, and end distance requirements without modification. The minimum values (1.2d0 for edges, 2.2d0 for pitch, 2.4d0 for gauge) are unchanged. The UK NA includes additional guidance on practical minimums for UK fabrication, typically adopting 40 mm as the nominal end distance for M20 bolts rather than the absolute minimum of 27 mm.
Related Pages
- EN 1993 Steel Design Overview
- European Steel Properties
- EN 1993 Beam Design Guide
- EN 1993 Column Buckling
- EN 1990 Load Combinations
- UK Steel Chemical Composition
- UK Steel Charpy Values
Educational reference only. All design values are per BS EN 1993-1-1:2005 + UK National Annex and BS EN 10025-2:2019. Verify all values against the current editions of the standards and the applicable National Annex for your project jurisdiction. Designs must be independently verified by a Chartered Structural Engineer registered with the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE). Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.