Minimum Spacing and Edge Distances — Table 3.3

Where d₀ = hole diameter and t = the minimum plate thickness.

Minimum Values by Bolt Size

Standard practice for M20: e₁ = e₂ = 30-40 mm, p₁ = 60-80 mm, p₂ = 60-80 mm.

Maximum Spacing Requirements

The maximum limits prevent plate buckling between bolts in compression zones:

• Maximum p₁ = min(14 × t_comp, 200 mm) — parallel to load
• Maximum p₂ = min(14 × t_comp, 200 mm) — perpendicular to load
• Maximum e₁, e₂ = 4 × t + 40 mm

For a 10 mm thick compression plate:

• Maximum p₁ = min(14 × 10, 200) = 140 mm
• Maximum e₁ = 4 × 10 + 40 = 80 mm

For a 20 mm thick plate:

• Maximum p₁ = min(14 × 20, 200) = 200 mm (capped)
• Maximum e₁ = 4 × 20 + 40 = 120 mm

Special Hole Types — Clause 3.6.2

Oversize Holes

Oversize holes are used in slip-resistant connections to facilitate erection tolerances.

Short Slotted Holes

For short slotted holes (parallel to load direction), increase p₁ by the slot length minus the standard clearance.

Edge Distance and Spacing — Practical Guidance

Standard Connection Layouts

Corrosion and Fire Protection Allowance

For galvanized connections, add 3 mm to all edge distances to account for the galvanizing coating thickness. For fire-protected connections, ensure adequate clearance for fireproofing.

Design Applications

Common Design Scenarios

This reference covers structural design scenarios commonly encountered in structural steel design practice:

• Strength verification: Check member or connection capacity against factored loads per the applicable design code
• Serviceability checks: Verify deflections, vibrations, and other serviceability criteria
• Code compliance: Ensure design meets all provisions of the governing standard
• Connection detailing: Verify weld sizes, bolt quantities, and edge distances

Related Design Considerations

• System behavior: consider the interaction between members and connections
• Load paths: verify that forces can be transferred through the structure to the foundations
• Constructability: check that the design can be fabricated and erected practically
• Cost optimisation: evaluate alternative sections or connection types for economy

Worked Example

Problem: Verify a typical steel member for the following conditions:

Typical span: 6.0 m | Load: service loads per applicable code | Section: common section in this category

Design Check:

1. Determine governing load combination (ULS or SLS per EN 1990)
2. Calculate maximum internal forces (moment, shear, axial)
3. Compute nominal capacity per code provisions
4. Apply resistance/safety factors
5. Verify interaction if combined forces exist

Result: Use the results from the Steel Calculator tool to verify design adequacy.

Frequently Asked Questions

What European Standard governs structural steel design?

EN 1993 (Eurocode 3: Design of Steel Structures) is the primary standard for structural steel design in Europe. EN 1993-1-1 covers general rules for buildings, EN 1993-1-8 addresses connection design, and EN 1993-1-2 covers fire design. The standard uses limit state design with partial safety factors (γM). National Annexes adapt parameters to each member state. Companion standards include EN 10025 for hot-rolled products, EN 1090 for execution, and EN 1994 for composite design.

What are the common steel grades used in European construction?

The most common steel grades for European construction are S235, S275, S355, S420, and S460 per EN 10025-2. S355 (minimum yield 355 MPa for t ≤ 16 mm) is the most widely used for structural applications. S275 is used for secondary members. S420 and S460 are quenched and tempered high-strength steels for weight-critical applications. Weathering steel (S355J2W) and fine-grain structural steels (EN 10025-3 and -4) are also available.

How does EN 1993 compare to other international steel design codes?

EN 1993, AISC 360 (US), AS 4100 (Australia), and CSA S16 (Canada) all use limit states design principles but differ in key details. EN 1993 uses partial safety factors (γM0 = 1.00, γM1 = 1.00, γM2 = 1.25) rather than resistance factors (φ). Buckling curves in EN 1993 follow the European Column Curve system (a0 to d) with 5 distinct curves, compared to AISC's single curve. EN 1993-1-8 has comprehensive connection design provisions including the component method for moment connections.

Frequently Asked Questions

What is the minimum edge distance for M20 bolts per EN 1993-1-8?

The minimum edge distance e₁ and e₂ for M20 bolts (d₀ = 22 mm) is 1.2 × 22 = 26.4 mm. In practice, use 30 mm minimum for standard details. For base plates with large anchor plates, 40-50 mm is more common.

Can I use bolt spacing less than the minimum per Table 3.3?

Per EN 1993-1-8 Clause 3.5(1), the minimum values in Table 3.3 are mandatory for design. Reduced spacing leads to reduced bearing resistance (lower α_b and k₁ factors) and increased risk of block shear failure. Spacing below 2.2 × d₀ is not permitted for structural connections.

Related Pages

• Bolt Bearing & Tearout — Bearing per EN 1993-1-8 Clause 3.6
• Bolt Group Capacity — Eccentric loads
• Bolt Torque Chart — Torque-tension values
• End Plate Connection — Moment connection
• All European References

Educational reference only. Spacing requirements per EN 1993-1-8:2005 Table 3.3. Verify against project specification and National Annex requirements. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

Design Resources

Calculator tools

• Bolt Torque Calculator
• Bolted Connection Calculator
• Splice Connection Calculator
• Steel Bolted Connection Calculator

Design guides

• Bolt Torque Worked Example
• Bolted Connection Checklist
• Bolted Connection Worked Example
• AISC Shear Tab Example
• EN 1993-1-8 Bolted Connection Worked Example