UK Shear Tab Design -- SCI P358 Simple Connections to EN 1993-1-8

The shear tab, known in UK practice as a fin plate connection, is the most common simple beam-to-column and beam-to-beam connection in multi-storey steel frames. It is classified as a nominally pinned joint per EN 1993-1-8 Clause 5.2.2, designed to transfer vertical shear only while accommodating end rotation through the ductility of the bolts in bearing. SCI Publication P358 "Joints in Steel Construction: Simple Joints to Eurocode 3" is the definitive UK design guide, providing standardised connection configurations with pre-calculated resistances. This reference presents the design method, limit states, and a fully worked design example for a fin plate connection in a UK office building.

Connection Configuration

A standard UK fin plate connection comprises:

• A rectangular plate (the fin plate or shear tab) welded to the supporting member (column flange or beam web) with two vertical fillet welds along the plate edges
• The plate projects beyond the support and is bolted to the web of the supported beam with a single vertical row of bolts (typically M20 Class 8.8, non-preloaded)
• The plate thickness is typically 8, 10, or 12 mm in S275 or S355 steel
• Bolt spacing and edge distances comply with EN 1993-1-8 Table 3.3 for nominally pinned behaviour

The fin plate is sized so that the bolt group is in single shear, with the plate bearing against the bolt shanks. The fillet welds are designed to transmit the full design shear from the plate into the supporting member.

Limit States for Fin Plate Connections

Per SCI P358 Section 6 and EN 1993-1-8, the following limit states must be verified:

Bolt Group Capacity

Shear resistance per bolt: Fv,Rd = alpha_v x fub x A / gamma_M2

Where alpha_v = 0.6 for Class 8.8 bolts with the shear plane passing through the unthreaded shank (shear plane in the threaded portion gives a reduced value of 0.5 in UK practice if the grip length positions the thread at the shear plane).

For an M20 Class 8.8 bolt with As = 245 mm^2: Fv,Rd = 0.6 x 800 x 245 / 1.25 = 94.1 kN per shear plane

Bearing resistance per bolt: Fb,Rd = k1 x alpha_b x fu x d x t / gamma_M2

Where:

• k1 accounts for edge distance in the direction perpendicular to load transfer
• alpha_b is the minimum of e1/(3 x d0), p1/(3 x d0) - 0.25, fub/fu, or 1.0
• d is the bolt diametre, t is the plate thickness, fu is the plate ultimate strength

Fin Plate Checks

Gross shear (plastic): Vpl,Rd = 0.577 x fy x hp x tp / gamma_M0

Net shear: The net shear area at the bolt holes must be checked: Vnet,Rd = 0.577 x fu x Anet / gamma_M2

Block tearing: The block tearing check considers the potential failure of a rectangular block of plate material, with shear rupture along the bolt line and tension rupture perpendicular to it: Veff,1,Rd = (fu x Ant / gamma_M2) + (fy x Anv / (sqrt(3) x gamma_M0))

Bending of the fin plate: The fin plate must have sufficient bending capacity to accommodate the rotational demand of the beam end without premature fracture. This is typically satisfied by limiting the plate thickness to a maximum of 0.42 x d (where d is the bolt diametre) for S275 plates, or 0.38 x d for S355 plates.

Weld Design

Fillet weld at plate edges: The two vertical fillet welds at the plate edges are designed for the combined shear and bending from the eccentric moment. The weld group is treated as a line element, with the unit force per millimetre of weld calculated from: Fwx = V x e x y / Ip (horizontal component from torsion) Fwy = V / Lw (vertical component from direct shear)

Resultant force per mm: Fw,R = sqrt(Fwx^2 + Fwy^2)

The weld size is selected so that Fw,R <= Fw,Rd, where Fw,Rd per mm is: Fw,Rd = a x fu / (sqrt(3) x beta_w x gamma_M2)

For a 6 mm fillet weld (throat a = 4.24 mm) with S355 plate and E42 electrode: Fw,Rd = 4.24 x 0.490 / (1.25) = 1.66 kN/mm per weld

Supporting Member Checks

The supporting column flange or beam web must be checked for:

• Shear: The applied shear must not exceed the plastic shear resistance of the supporting member
• Tying resistance: The fin plate must develop a tying force of at least 75 kN for structural integrity (building Class 2B per Approved Document A)

Standard Fin Plate Configurations per SCI P358

SCI P358 provides pre-calculated resistances for standard configurations, avoiding the need for detailed calculation in routine designs:

For S355 plate, capacities are approximately 15% higher due to the increased ultimate strength (fu = 510 MPa vs 430 MPa for S275).

Worked Example -- Fin Plate for UK Office Beam

A 406 x 178 x 54 UB in S355 supports a design shear VEd = 185 kN at the ultimate limit state. Design a fin plate connection to the column flange.

Step 1 -- Select standard configuration: Beam depth = 402.6 mm. Use SCI P358 standard: 260 x 90 x 10 plate in S275, 4 x M20 Class 8.8 bolts, 6 mm fillet welds. Published shear capacity = 320 kN > 185 kN -- OK by inspection.

Step 2 -- Verify bolt shear: 4 bolts in single shear. Shear per bolt = 185 / 4 = 46.3 kN. Fv,Rd per bolt = 94.1 kN. Utilisation = 46.3 / 94.1 = 0.49 -- OK.

Step 3 -- Verify bearing on fin plate: t = 10 mm, fu = 430 MPa (S275), d = 20 mm, d0 = 22 mm, e1 = 45 mm, e2 = 35 mm, p1 = 70 mm. alpha_b = min(45/(3x22), 70/(3x22)-0.25, 800/430, 1.0) = min(0.68, 0.81, 1.86, 1.0) = 0.68 k1 = min(2.8 x 35/22 - 1.7, 2.5) = min(2.75, 2.5) = 2.5 Fb,Rd = 2.5 x 0.68 x 430 x 20 x 10 / 1.25 = 116.9 kN per bolt. Utilisation = 46.3 / 116.9 = 0.40 -- OK.

Step 4 -- Verify weld: Weld length Lw = 260 mm each side (two welds). Eccentricity e = 45 mm (half plate width). Ip = 2 x 260^3 / 12 + 2 x 260 x 45^2 = 2,929,000 + 1,053,000 = 3,982,000 mm^3 Fwy = 185 / (2 x 260) = 0.356 kN/mm Fwx = 185 x 45 x 130 / 3,982,000 = 0.272 kN/mm Fw,R = sqrt(0.356^2 + 0.272^2) = 0.448 kN/mm Fw,Rd for 6 mm FW = 1.66 kN/mm. Utilisation = 0.448 / 1.66 = 0.27 -- OK.

Step 5 -- Verify tying resistance: Tying force required: 75 kN. SCI P358 published tying = 223 kN > 75 kN -- OK.

Design Resources

• UK End Plate Connection Design — Moment-resisting end plate joints
• UK Bolt Capacity Tables — Fv,Rd and Ft,Rd per EN 1993-1-8
• UK Weld Design Guide — Fillet weld capacity per EN 1993-1-8
• UK Connection Design Guide — Complete EN 1993-1-8 joint reference
• UK Steel Connection Types — Overview of UK connection practice

Frequently Asked Questions

Why are fin plates the most common beam connection in UK multi-storey frames?

Fin plates are simple to fabricate (a rectangular plate with two fillet welds and drilled holes), quick to erect on site (the beam is offered up between the plate and a loose plate or angle on the other side), and they reliably behave as pinned connections, decoupling the beam design from the column design. Their ductility through bolt bearing provides robustness against accidental loads without requiring explicit structural integrity calculations for routine configurations. They are also the most economical connection type, at approximately 35-55 pounds per connection for a typical beam (fabricated and delivered, excl. erection).

What plate thickness should I use for a fin plate connection?

UK practice uses 10 mm plate as standard for most fin plates, with 8 mm used for lighter beams (shear < 100 kN) and 12 mm for heavy beams (shear > 400 kN). The plate thickness should not exceed 0.42 x d for S275 (8.4 mm maximum for M20 bolts) to ensure the plate yields in bending before the bolts fracture in shear, providing ductile behaviour. For S355 plate, the maximum thickness for the same ductility requirement is 0.38 x d (7.6 mm for M20). Where a thicker plate is required for shear or bearing capacity, the rotational capacity must be verified by a more detailed calculation or by using a different connection type (flexible end plate or web cleat).

Can I use preloaded bolts in a fin plate connection?

Fin plates are designed as nominally pinned connections where slip at the bolt holes is not detrimental to the structural behaviour (the beam end rotates, and the bolt holes accommodate this through bearing deformation). Preloaded bolts are not required and would add cost (PIVT, calibrated wrenches, inspection) without structural benefit. The only exception is when the fin plate also serves as the tying connection for structural integrity in a building where slip is unacceptable under the accidental load combination -- but even then, UK practice typically increases the number of bolts rather than specifying preload.

What is the SCI P358 Green Book and why should I use it?

SCI P358 "Joints in Steel Construction: Simple Joints to Eurocode 3" (commonly called the Green Book) is the standard UK reference for simple connection design. It contains pre-calculated tables for fin plates, flexible end plates, web cleats, and column base plates, covering the full range of UK beam and column sizes. Using the Green Book tables eliminates the need for limit state calculations in routine designs while ensuring full compliance with EN 1993-1-8 and the UK NA. The tables include shear capacity, tying resistance, and detailing requirements for each configuration.

Educational reference only. All design values are per BS EN 1993-1-8:2005 + UK National Annex and SCI P358. 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.