UK Shear Tab (Fin Plate) Connection Design — EN 1993-1-8 + UK NA
Design of a fin plate (shear tab) connection per EN 1993-1-8 Clause 6.2.6 with UK National Annex. Worked example for a 533UB beam connecting to a supporting member via a welded fin plate and bolted web connection. Covers the SCI P358 method for simple connections in UK steel frames.
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Fin Plate Connection per EN 1993-1-8 Clause 6.2.6
The fin plate (shear tab) is a welded plate connection to the supporting member with bolted connections to the supported beam web. It is classified as a nominally pinned (simple) connection.
Design Checks Required
| Component | Check | EN 1993-1-8 Clause |
|---|---|---|
| Bolts in shear | Fv,Rd | Table 3.4 |
| Bolts in bearing (fin plate) | Fb,Rd | Clause 3.6 |
| Bolts in bearing (beam web) | Fb,Rd | Clause 3.6 |
| Fin plate in shear | Vpl,Rd | Clause 3.10 |
| Fin plate in bending | — | SCI P358 guidance |
| Fin plate block tearing | Veff,Rd | Clause 3.10.2 |
| Fin plate weld | Fw,Rd | Clause 4.5 |
| Beam web in shear | Vpl,Rd | EN 1993-1-1 Cl. 6.2.6 |
| Beam web block tearing | Veff,Rd | Clause 3.10.2 |
Worked Example — 533UB Fin Plate Connection
Connection details:
- Supported beam: 533UB in S355
- Support: column or girder
- Fin plate: 200 × 100 × 10 mm, S355
- Bolts: 4 × M20 Class 8.8 in single shear (2 rows × 2 columns)
- Fillet weld: 8 mm leg (5.6 mm throat) on both sides
Step 1 — Bolt Shear Check (Threads in Plane)
Fv,Rd = 47.0 kN per bolt (M20, 8.8, single shear, threads in plane)
Shear plane: 1 n = 4 bolts
Total shear resistance: VRd = 4 × 47.0 = 188 kN
Step 2 — Bearing Check (Fin Plate, t = 10 mm, S355, fu = 470 MPa)
Standard spacings: e1 = 40 mm, e2 = 30 mm, p1 = 70 mm, d0 = 22 mm
End bolt: αb = min(40/(3×22), 70/(3×22) − 0.25, 800/470, 1.0) = min(0.606, 0.811, 1.702, 1.0) = 0.606
k1 = min(2.8×30/22 − 1.7, 2.5) = min(2.118, 2.5) = 2.118
Fb,Rd (end) = 2.118 × 0.606 × 470 × 20 × 10 / 1.25 = 96,500 N = 96.5 kN
Step 3 — Fin Plate Shear Resistance (Clause 3.10)
Shear area: Av = h_plate × t = 200 × 10 = 2,000 mm²
Vpl,Rd = Av × fy / (√3 × γM0) = 2,000 × 355 / 1.732 = 710,000 / 1.732 = 410 kN
Step 4 — Fillet Weld Design
8 mm leg, throat a = 5.6 mm, both sides, length = 200 mm
Fw,Rd = a × fu / (√3 × βw × γM2) = 5.6 × 470 / (1.732 × 0.85 × 1.25) = 2,632 / 1.84 = 1,430 N/mm = 1.43 kN/mm
Total weld resistance: 2 × 200 × 1.43 = 572 kN
Summary
| Component | Resistance (kN) | Governing? |
|---|---|---|
| Bolt shear (4 × M20 8.8) | 188 | Governs |
| Bearing — fin plate (end bolt) | 96.5/bolt | No |
| Bearing — beam web | Similar — check separately | No |
| Fin plate shear | 410 | No |
| Weld (8 mm, both sides) | 572 | No |
Capacity: VRd = 188 kN (governed by bolt shear). This is adequate for a 533UB with typical reactions of 100-150 kN at 6-8 m spans with standard floor loadings.
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 typical capacity of a fin plate connection in UK practice?
A standard fin plate connection with 4 × M20 Class 8.8 bolts in S355 steel provides approximately 180-200 kN shear capacity (governed by bolt shear with threads in the shear plane). With 6 × M20 bolts: 280-300 kN. With 4 × M24 bolts: 250-270 kN. These capacities are per SCI P358 design tables. The bolt shear check (threads in plane) almost always governs; plate bearing and weld resistance are typically higher.
How many bolts are standard for a fin plate connection in UK steel frames?
UK standard practice per SCI P358 uses: 2 bolts (minimum, very light connection), 3 bolts (standard for secondary beams, 406UB or smaller), 4 bolts (standard for primary beams, 533UB-610UB), and 5-6 bolts (heavy beams, large spans). The bolt rows are arranged in a single vertical line (2-column gauge) for 4-bolt connections. M20 Class 8.8 is the default bolt specification.
What is the minimum fin plate thickness for a UK shear tab?
The minimum fin plate thickness is typically 8 mm for light connections, 10 mm for standard connections (4 × M20), and 12-15 mm for heavy connections. The plate must satisfy: (1) bearing resistance — thicker plate = higher Fb,Rd per bolt, (2) shear resistance — Av × fy/(√3 × γM0) ≥ VEd, (3) block tearing — checked per Clause 3.10.2. The plate also requires adequate stiffness for erection stability — a 10 mm thick plate is the UK standard for 4-bolt fin plates.
Does the UK NA modify fin plate connection design?
The UK NA to BS EN 1993-1-8 does not specifically modify fin plate design rules. The design follows the standard EN 1993-1-8 provisions for bolt groups (Clause 3.6), shear resistance (Clause 3.10), and welded joints (Clause 4). The UK NA confirms γM2 = 1.25 for bolts and welds. SCI P358 (Joint Design in Steel Construction) is the definitive UK design guide for fin plates and other simple connections.
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.