SCI P358 — The UK Simple Connections Standard

SCI P358 (published 2011, reprinted with amendments 2014) provides standardised designs for nominally pinned connections in accordance with BS EN 1993-1-8. It is the successor to the "Green Book" (SCI P212 — Joints in Simple Construction, to BS 5950) and is the primary reference for UK simple connection design.

Key principles of simple connections per EN 1993-1-8 Clause 5.1.1:

• The connection transmits shear only (no significant moment transfer)
• The connection has sufficient rotation capacity to accommodate end rotations (approximately 0.02-0.03 rad for simply supported beams)
• The connection does not adversely affect the global structural analysis assumptions
• Joints are designed as "simple" per the UK NA — rotation capacity is verified by compliance with SCI P358 standardised geometries

Connection Type 1: Fin Plate (Shear Tab)

The most common UK simple beam-to-column and beam-to-beam connection.

Configuration:

• Vertical plate welded to the supporting member (column flange or web)
• Beams bolted to the fin plate through the beam web
• Bolts typically M20, Class 8.8, in single shear
• Standard plate thickness 8-12 mm in S275

Standard UK geometry (SCI P358):

Design checks (per SCI P358):

1. Bolt shear (EN 1993-1-8 Table 3.4)
2. Bolt bearing on fin plate and beam web (Table 3.4)
3. Fin plate shear (gross and net section)
4. Fin plate block tearing (Clause 3.10.2)
5. Beam web bearing and block tearing
6. Fin plate buckling (Clause 6.3.1 — buckling length = 0.6 x distance from weld to first bolt row)
7. Weld to supporting member (directional method, Clause 4.5.3.2)
8. Supporting member (column web) — bearing, shear, and punching

Typical UK capacities (M20, 8.8 bolts, 10 mm S275 fin plate, 200 mm long, 4 bolts):

Shear resistance approximately 200-350 kN, depending on bolt configuration and beam web thickness.

Connection Type 2: Partial-Depth End Plate

The second most common UK simple connection — used where the beam is prepared with a welded end plate in the fabrication shop.

Configuration:

• End plate welded to the beam web only (plate height = beam depth between fillets, not full depth)
• End plate bolted to the supporting column flange or web
• Bolts typically M20, Class 8.8

Standard UK geometry (SCI P358):

Advantages over fin plate:

• Can carry higher shear (two vertical bolt lines instead of one)
• Better for deep beams (bolt group has larger lever arm resistances)
• Easier beam erection (bolts at beam ends, not through web)
• Less site drilling required

Disadvantages:

• More fabrication (end plate welded in shop)
• Beam must be cut to exact length (no site adjustment)
• Clearance issues with column web stiffeners

Connection Type 3: Full-Depth End Plate

Used where higher shear capacity is required or where the beam depth exceeds the standard partial-depth end plate range.

Configuration:

• End plate extends to the full beam depth, welded to both flanges and web
• Typically 15-25 mm plate thickness

Key difference from partial-depth: The full-depth plate engages the beam flanges, providing some nominal moment restraint. For nominally pinned design, the plate thickness must not exceed d/10 (approximately) to ensure adequate flexibility for rotation. Thicker plates or plates with bolts outside the tension flange produce moment-resisting behaviour.

Connection Type 4: Web Cleats (Angle Connections)

Used for beam-to-beam connections and where the connection geometry favours bolted angles.

Configuration:

• Two angle sections (typically 90 x 90 x 8 or 100 x 100 x 10 RSA) bolted to the beam web and the supporting member
• Bolts through both legs of each angle

Standard UK geometry (SCI P358):

Advantages:

• No site welding required (fully bolted)
• Tolerances can be accommodated during erection (oversized holes in the outstanding leg)
• Can be installed with the beam in place

Disadvantages:

• Lower shear capacity than fin plate or end plate
• More components (two angles + bolts)
• Bolt clashes with other connections on the same face

Connection Type 5: Column Splice

Column splices in UK multi-storey frames are typically designed as nominally pinned bearing splices.

Configuration:

• Division plates (end plates) on both column ends, butted together
• Flange cover plates and web cover plates bolted
• Compression transferred by bearing between division plates (machined or fitted contact)
• Cover plates provide lateral location and nominal tension capacity for robustness

Standard UK column splice (SCI P358):

UK Connection Selection Guide

Tie Force Requirements — UK Building Regulations

Approved Document A (Structure) requires that all connections in Class 2B buildings (5+ storeys or > 15 m) have a minimum horizontal tie force capacity:

• Peripheral ties: Ft = 75 kN (or 0.25 x (gk + qk) x span, whichever is greater)
• Internal ties: Ft = 0.5 x (gk + qk) x span x storey height, but >= 75 kN
• Column ties: Ft = largest beam reaction connected to the column

SCI P358 Table G.1 provides pre-calculated tie resistances for standardised connection details. For fin plate connections, the tie force is typically carried by the fin plate in tension plus the bolts in bearing. The weld to the supporting member must also transfer the tie force. Where the standard connection detail cannot achieve the required tie force, supplementary tie elements (flat plates, angles) may be added.

Frequently Asked Questions

When should I use the full "Green Book" (SCI P212/SCI P358) connection design rather than a rule-of-thumb?

Always. SCI P358 provides verified, tested connection resistances for standardised UK geometries. Engineering judgment (rule-of-thumb) is not a substitute for verified design resistances. The cost difference between a 6-bolt and 8-bolt fin plate is minimal (a few pounds per connection), but the consequence of an under-designed connection failing in shear is catastrophic (progressive collapse risk). UK checking engineers and Building Control will require SCI P358-compliant connection calculations for all primary beam connections. Rule-of-thumb (e.g., "4 M20 bolts good for 200 kN") should be used only for preliminary sizing, never for final design.

How do I connect a beam to a hollow section column?

Hollow section columns (SHS/RHS) present a connection challenge because there is no internal access for bolting through the column. UK solutions: (1) Flowdrill (friction drilling) to create a threaded boss in the column wall — then bolt through the fin plate/end plate into the threaded boss (Lindapter Hollo-Bolt is a proprietary alternative); (2) welded fin plate or end plate to the column face (requires full-strength weld and column wall check for punching/local yielding); (3) through-plate passing through the column with the beam connecting to the projecting plate each side; (4) blind bolts (Lindapter, BoxBolt). Flowdrill is the most common UK solution for SHS columns in building frames.

What are the UK inspection requirements for bolted connections?

BS EN 1090-2 (Execution Class 2, standard for UK buildings) requires: (1) visual inspection of all bolts for correct size, grade marking, and washer placement; (2) snug-tight condition confirmed by visual inspection or feeler gauge (gap <= 2 mm between plies); (3) for preloaded bolts (slip-resistant connections): 5 % minimum sampling of bolt torque/tension via calibrated wrench or direct tension indicator (DTI) washers, plus visual check of DTI squirt-out; (4) verification that the number and arrangement of bolts match the design drawings. Full tightening records are not required for snug-tight bolts (standard for UK simple connections) but are required for preloaded bolts per BS EN 1090-2 Annex H.

How does the UK NA to EN 1993-1-8 affect connection design?

The UK NA adopts all EN 1993-1-8 recommended values for bolt resistances without modification (gamma_M2 = 1.25, alpha_v = 0.6 for threads in shear plane). The main UK NA impact is: (1) adoption of SCI P358 as the recognised UK standard for simple connections (the "verified standard details" route in Clause 5.1.1(2)); (2) UK practice uses BS EN 1090-2 for execution, which is more prescriptive about bolt tightening than the EN 1993-1-8 default; (3) tie force requirements from UK Building Regulations Approved Document A impose additional tensile checks beyond the standard shear connection design.

Related Pages

• UK Connection Design Guide — EN 1993-1-8 full guide
• UK Moment Connection Design — SCI P398 moment joints
• UK Fin Plate Connection — Fin plate detailed design
• UK End Plate Connection — Partial-depth and full-depth end plates
• UK HSS Connection Guide — Hollow section connections
• UK Weld Design Guide — Fillet weld design to EN 1993-1-8
• UK Bolt Capacity Tables — Class 8.8 and 10.9 bolt resistances

Educational reference only. Connection standardised geometries and resistances are per SCI P358 (Joints in Steel Construction: Simple Joints to Eurocode 3, 2011, reprinted 2014) and BS EN 1993-1-8:2005 with UK National Annex. Verify all resistances against the current editions of the standards and against project-specific connection geometry. 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.