EN 1993-1-8 Connection Design
Bolted Beam Splice Design (EN 1993-1-8)
Design of bolted beam splices under combined shear and moment per EN 1993-1-8. Worked example with IPE 450, splice plate design, and force path analysis.
Download EN 1993-1-8 Cheatsheet (free PDF)Figure: Force flow — tension in upper bolts, compression strut at bottom, moment couple transferred via endplate.
When to Use This Connection
Bolted beam splices are used where: beam length exceeds available section length; the connection must be made in a zone of low moment (ideally mid-span or near point of contraflexure); or site constraints prevent full-welded connections. Typical applications: portal frame rafters spliced for transport, multi-storey beams, and crane gantry beams.
Worked Example
Configuration: IPE 450 beam spliced at point of contraflexure; MEd = 85 kNm; VEd = 120 kN; S355; 8.8 M20 bolts; splice plates 200×10mm.
Design moment: MEd = 85 kNm; VEd = 120 kN
Step 1 — Determine design forces
EN 1993-1-8
MEd, VEd from frame analysis
At splice location: axial NEd is negligible. Design for MEd and VEd simultaneously.
Step 2 — Splice plate sizing
EN 1993-1-8 3.5
VRd = Av·fy / (√3·γM0)
200×10mm splice plate (one per side): Av = 2000 mm² → VRd = 410 kN.
Step 3 — Bolt group design
EN 1993-1-8 3.4
Fv = VEd / nbolts
6-bolt group (3 per side): Fv = 20 kN/bolt. M20 8.8: Fv,Rd = 94.1 kN.
Step 4 — Combined shear+tension check
EN 1993-1-8 3.4.1(4)
Fv,Ed/Fv,Rd + Ft,Ed/Ft,Rd ≤ 1.0
Verify combined loading for all bolts in the group.
Bolt Capacity Reference
γM2 = 1.25; fub per EN ISO 4014/4017; Ft,Rd per EN 1993-1-8 3.4.1; Fv,Rd in double shear
| Bolt | Grade | d (mm) | As (mm²) | Ft,Rd (kN) | Fv,Rd (kN) |
|---|---|---|---|---|---|
| M16 | 8.8 | 16 | 157 | 113.0 | 88.9 |
| M16 | 10.9 | 16 | 157 | 141.3 | 88.9 |
| M20 | 8.8 | 20 | 245 | 176.4 | 138.2 |
| M20 | 10.9 | 20 | 245 | 220.5 | 138.2 |
| M24 | 8.8 | 24 | 353 | 254.2 | 199.0 |
| M24 | 10.9 | 24 | 353 | 317.7 | 199.0 |
Common Failure Modes
Bolt shear failure
Governed by single shear in asymmetric splice designs. Always use splice plates on both flanges.
Splice plate yielding
Thin splice plates (<8mm) buckle under compression. Use ≥ 10mm for S355.
Web buckling at splice
Web splice plates must extend ≥ 50% of web depth.
Prying action in thin splice plates
Check for prying per EN 1993-1-8 Annex A.
Detailing Gotchas
- Splice location: place at point of contraflexure or ≤ 0.2L from support for minimum moment zone
- Web splice plate: minimum thickness 6mm; width ≤ beam web depth − 2 × fillet radius
- Bolt pattern: staggered layout reduces stress concentrations in thin webs
- Fillet weld between splice plates and beam web: use 6mm fillet if shop-welded