EN 1993-1-8 Connection Design
Endplate Moment Connection Design (EN 1993-1-8)
Step-by-step endplate moment connection design to EN 1993-1-8. Worked example with IPE 400–HEA 300, bolt tables, failure modes, and a free FrameAI demo.
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
Extended endplate connections are used where a full moment continuity is required between beam and column. Typical applications: portal frame eaves connections, multi-storey frames where frame action is assumed, and continuous beam systems where moment transfer is needed.
Worked Example
Configuration: IPE 400 beam welded to column flange; 10mm extended flush endplate; M20 bolts grade 10.9; S355 steel.
Design moment: MEd = 285 kNm (from frame analysis, ULS combination)
Step 1 — Bolt row effective lengths
EN 1993-1-8, Table 6.4
ℓeff = α · m
For non-haunch config, α = 4; m = distance from bolt axis to flange centreline.
Step 2 — Bolt tension resistance
EN 1993-1-8, 3.4.1
Ft,Rd = k₂·fub·As / γM2
M20 10.9: As = 245 mm², fub = 1000 N/mm², k₂ = 0.9, γM2 = 1.25 → Ft,Rd = 176.4 kN/bolt
Step 3 — Column flange in bending
EN 1993-1-8, §6.3
MRd = ℓeff·t²·fy / (6·γM0)
T-stub equivalent method. With m = 30 mm, pitch p = 60 mm: ℓeff,b = 2m + p.
Step 4 — Moment resistance summation
EN 1993-1-8, 6.2.7.2
Σ Fi · zi
Sum all active bolt rows using lever arms from neutral axis (centre of compression zone).
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 rupture in tension
Most common in over-stressed 8.8 bolts. Use 10.9 or add a bolt row.
Column flange bending
Check using T-stub model. Thick column flanges (≥20mm for HEA columns) usually sufficient.
Endplate yielding
10mm endplate in S355 is borderline for M > 250 kNm. Increase to 12 or 15mm.
Weld failure at beam flange
Full penetration weld required per EN 1993-1-8 Table 4.1. Use fillet weld for web only.
Web panel shear in column
Check EN 1993-1-8 §6.2.6. Reinforce with doubler plate if VEd > Vpl,Rd.
Detailing Gotchas
- Extended endplate should protrude ≥ 40mm beyond the beam flange (EN 1993-1-8 6.2.5 note)
- Minimum bolt spacing: 2.2d₀ from centre to edge (d₀ = bolt hole diameter)
- Tight endplate gaps (≤4mm) can be assumed as bearing-type. Larger gaps need fin plate or haunch.
- Haunch geometry: the fictitious compression strut must clear the column web AND the stiffener if fitted.