EN 1993 End Plate Connection — Moment Connection per Eurocode 3

Complete guide to end plate moment connections per EN 1993-1-8:2005 Clause 6.2. T-stub model for tension zone, bolt row force distribution, compression zone verification, end plate and column flange bending. Worked example with IPE 300 beam and end plate.

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Connection Types — EN 1993-1-8 Clause 6.2

Flush End Plate

The end plate is contained within the beam depth. Economical for moderate moments. Tension bolts are confined to the beam tension flange region.

Extended End Plate

The end plate extends beyond the beam tension flange. Allows an extra row of bolts above the tension flange. Higher moment capacity, suitable for rigid frames.

Type Typical Depth Moment Capacity Cost Factor
Flush end plate ≈ beam depth 0.5-0.7 × M_pl,Rd 1.0
Extended end plate beam + 100 mm 0.8-1.2 × M_pl,Rd 1.3-1.5
Bolted flange plate — 1.0-1.3 × M_pl,Rd 1.5-1.8

T-Stub Model — Clause 6.2.4

The tension zone is modelled as equivalent T-stubs representing:

  1. Column flange in bending (T-stub 1)
  2. End plate in bending (T-stub 2)
  3. Bolts in tension

T-Stub Effective Length

For an extended end plate, the effective length l_eff of the T-stub per bolt row:

Bolt Row Location l_eff (circular pattern) l_eff (non-circular) Governing
Row above flange (ext) 2π × m_x 4 × m_x + 1.25 × e_x min
Row below flange 2π × m α × m (from geometry) min
Inner row (flush) 2π × m 4 × m + 1.25 × e min

T-Stub Resistance Modes

Three failure modes per EN 1993-1-8 Table 6.2:

Mode Failure Description Resistance F_T,Rd
1 Complete flange yielding (4 × M_pl,1,Rd) / m
2 Bolt failure with flange yielding (2 × M_pl,2,Rd + n × ΣF_t,Rd) / (m+n)
3 Bolt failure only ΣF_t,Rd

Bolt Row Force Distribution — Clause 6.2.7

  1. Calculate the effective tension resistance of each bolt row (F_t,Rd)
  2. Distribute total tension force among rows:
    • First row (at beam tension flange): takes maximum tension
    • Subsequent rows: limited by available lever arm
  3. The total tension force centroid determines the lever arm z between tension and compression

Lever Arm z

z = distance from centre of compression (at beam compression flange centreline) to the centroid of the bolt tension force.

For flush end plates with 2 bolt rows:

Row Configuration Lever Arm z Typical Utilization
2 rows, 70 mm pitch ~270 mm 0.65
3 rows, 70 mm pitch ~320 mm 0.80
Extended 4 rows ~380 mm 0.95

Worked Example — IPE 300 Flush End Plate

Parameter Value
Beam IPE 300, S355
End plate 250 × 150 × 12 mm, S355
Bolts 4 × M20 8.8 (2 rows)
M_pl,Rd (beam) 223.1 kN·m
Bolt row pitch p₁ 70 mm
End distance e₁ 35 mm

Tension Zone (T-stub)

Mode Resistance per row Total F_t,Rd (2 rows)
1 180 kN —
2 165 kN —
3 188 kN —
Governing (Mode 2) 165 kN/row 330 kN

Moment Resistance

Lever arm z ≈ 270 mm (from comp. flange centre to tension bolt centroid)

M_j,Rd = 330 × 0.270 = 89.1 kN·m

Utilization: 89.1 / 223.1 = 0.40 relative to beam capacity.

Increasing to an extended end plate with 4 bolts in tension gives M_j,Rd ≈ 160 kN·m.

Compression Zone — Clause 6.2.6

The compression zone resistance is the minimum of:

F_c,fb,Rd = f_y,wc × b_eff,c,wc × t_wc / γ_M0

If the column web is unstiffened, the compression resistance may be significantly less than the beam capacity, requiring transverse stiffeners.

Frequently Asked Questions

What is the difference between flush and extended end plate connections?

A flush end plate stops at the beam tension flange level, while an extended end plate projects beyond the beam flange to accommodate extra bolt rows. Extended end plates provide 40-70% higher moment capacity and are used for rigid connections in moment frames. Flush end plates are more economical and are used for semi-rigid and pinned connections.

When are column web stiffeners required for end plate connections?

Column web stiffeners are required when the column web compression (or tension) resistance is less than the applied flange force. Per EN 1993-1-8 Clause 6.2.6.2, stiffeners are needed when F_c,fb,Rd < F_c,Ed. For beam-to-column connections where the beam depth exceeds 75% of the column depth, stiffeners are almost always required.

Related Pages

Educational reference only. Design per EN 1993-1-8:2005 Clause 6.2. T-stub model per Table 6.2. Verify end plate thickness and bolt class against applied moment. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

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