UK Steel Framing Guide — SCI P365, Simple Construction & Typical Details

Complete reference for UK structural steel framing practice per EN 1993-1-1 and SCI P365. Covers simple construction philosophy, standard beam-to-column connection types (flexible end plates, fin plates, web cleats), column splice design, bracing system selection, composite floor decking, and a fully worked 3-bay office frame sizing example with yield checks under UK loading. All clause references to BS EN 1993-1-1:2005 + UK National Annex.

Quick access: UK Beam Sizes | UK Connection Design | UK Column Design | UK Beam Design Example | All UK References

1. The UK Structural Steelwork Supply Chain

Understanding how UK steel frames are procured, designed, and erected is the starting point for efficient framing:

In UK practice, the structural engineer typically specifies member sizes, grid, and stability system on the general arrangement drawings. The steelwork contractor then designs and details the connections — usually to the SCI/BCSA 'Green Book' series (P358 for simple connections, P398 for moment-resisting connections, P207 for column splices). This division of responsibility is standard under the BCSA National Structural Steelwork Specification.

The steelwork contractor must hold BS EN 1090-1 certification (Factory Production Control) and CE/UKCA mark the fabricated steel. Execution Class EXC2 is the default for building structures; EXC3 applies to fatigue-loaded or high-consequence structures.

2. Simple Construction — The UK Default

Philosophy

Simple construction is the assumption that beam-to-column connections transfer only vertical shear — no moment. The beams are analysed as simply supported, columns carry predominantly axial load with nominal eccentricity moments from the connection detail, and lateral stability comes from a separate bracing system or core.

This approach is codified in EN 1993-1-8 Clause 5.1.1(3): a nominally pinned connection must be capable of transmitting the design shear forces without developing significant moments that would adversely affect any part of the structure. In practical UK terms, a simple connection must have sufficient rotation capacity to allow the beam end to rotate under load without developing a moment exceeding 5% of the beam's plastic moment capacity.

Why It Dominates UK Practice

1. Fabrication economy: Simple connections use standard plates and angles cut from stock — no column stiffeners, no shop-welded haunches.
2. Erection speed: Beams drop in between columns on pre-set seating cleats or erection bolts. A typical 2-bay floor can be erected by a 4-man gang in a single day.
3. Analysis simplicity: Simply supported beam design is deterministic; no need for iterative frame analysis to resolve moment distribution.
4. Proven performance: SCI P365 tabulates resistances for all standard UK sections in S275 and S355, so member sizing reduces to look-up rather than from-first-principles calculation.

When Simple Construction Does Not Apply

• Buildings over approximately 12 storeys where drift control requires moment frames
• Long-span beams (>15 m) where simply supported deflection becomes uneconomic
• Architecturally expressed steel where connection visibility demands a rigid appearance

3. SCI P365 — The UK Design Data Bible

SCI Publication P365 Steel Building Design: Design Data (commonly called "the Blue Book" in its print form, though the current edition uses the SCI online member resistance tool) provides pre-calculated design resistances for every standard UK open section:

What P365 Covers

Using P365 in Practice

To size a UK floor beam, a designer would typically:

1. Calculate the factored UDL: w_Ed = 1.35G_k + 1.5Q_k (or the 6.10a/b expressions from UK NA to EN 1990)
2. Compute M_Ed = w_Ed * L^2 / 8
3. Open P365 to the S355 beam bending table, find the first section where M_c,Rd exceeds M_Ed
4. Check shear (V_Ed < V_pl,Rd) and deflection (delta < L/360 for composite floors, L/200 for non-composite)
5. Confirm the section chosen has adequate buckling resistance for the unbraced length during construction

The SCI no longer publishes P365 as a static PDF — it is an online web tool at steelconstruction.info, continuously updated to match the latest Eurocode amendments and National Annex revisions.

4. UK Beam-to-Column Connections — The Big Three

4.1 Flexible End Plates (Partial-Depth)

The most common UK connection type. A plate 8 mm or 10 mm thick, typically 60% of the beam depth, is fillet-welded to the beam web in the shop. On site, the beam is positioned and bolted through the plate to the column flange or web using M20 Grade 8.8 bolts in 22 mm clearance holes.

Design rule (SCI P358): The partial-depth end plate is designed as a vertical cantilever plate in bending with the bolt group below the beam bottom flange. The critical checks are bolt shear, bolt bearing on the plate, plate bending (gross section), and the supporting column web panel shear.

4.2 Fin Plates

A single vertical plate shop-welded to the face of the column flange or web. The beam web is site-bolted to the fin plate. Popular for secondary beams framing into column webs where access for end plates is restricted.

Advantages:

• Simple to fabricate (single plate, single weld)
• Good site adjustment (beam can be shimmed between fin plate and web)
• Standardised for notch details to clear column flanges

Disadvantages:

• Single shear plane reduces bolt group capacity compared to double-cleat arrangements
• Notch in beam top flange required to clear column flange — reduces shear and bending capacity at the cope
• Limited to moderate shear demands (typically < 250 kN unless deepened)

4.3 Web Cleats (Double Angle Cleats)

A pair of angles (typically 90x90x8 or 100x100x10 RSA) bolted to the beam web and column face. Common for retrofit work, heavy beam connections, and situations where the beam depth allows double-row bolting.

Design rule: The outstanding legs of the angles are checked for bending (lever arm between bolt lines) and the bolt group capacity is evaluated for double-shear with the angles in bearing. Web cleats provide inherent rotational ductility because the angle legs can flex under rotation.

5. Column Design in UK Framing

5.1 UK Column Sections

UK columns predominantly use UC (Universal Column) sections in S355 or S460 steel:

Values are indicative. Check SCI P365 for the exact section with correct effective length and buckling curve.

5.2 Column Splices

UK column splices are typically located 600 mm above floor level (clear of the beam-to-column connection zone). The splice must transmit axial load plus nominal moment from eccentricity (minimum 100 mm assumed eccentricity unless a more precise analysis is performed).

Standard UK column splices use:

• Flange cover plates — 2 plates sized to transfer the flange force (typically 50–60% of axial load per flange)
• Web splice plates — 2 plates or a single plate transferring the remaining force through the web
• Division plates — used when column sizes change; the smaller column bears on a plate that spans between the larger column flanges

SCI P207 provides standardised splice designs. For columns in S355, Grade 8.8 M20 or M24 bolts are standard in 22 mm or 26 mm clearance holes.

6. Bracing Systems

6.1 Vertical Bracing

The UK standard for vertical bracing in simple-construction frames is X-bracing or chevron (V/inverted-V) bracing in selected bays, typically at the building perimeter and around the lift/stair core.

Rod bracing (Macalloy / tension rods): Prevalent in UK portal frame and industrial buildings. Circular hollow sections or solid bars with fork-end connectors. Installed with a turnbuckle to remove slack. Only effective in tension — the designer must verify both orthogonal directions are independently braced.

Section bracing (RHS/SHS): Used where compression resistance is needed (both directions in a single frame). Typically 100x100x5 SHS to 200x200x8 SHS in S355. Connections are welded end plates or gusset plates with Grade 8.8 bolts.

6.2 Horizontal Diaphragms

The floor diaphragm transfers horizontal wind and stability loads from the facade to the vertical bracing system. In UK practice, composite metal deck floors with in-situ concrete topping form an effective rigid diaphragm, provided:

• The minimum concrete thickness is 70 mm over the deck profile (typically 130 mm total for ComFlor 60)
• Reinforcement mesh (A142 or A193) is provided as minimum anti-crack reinforcement
• Shear studs (19 mm diameter, typically 95 or 125 mm as-welded height) connect the beam to the slab at 300 mm centres for composite action and diaphragm chord force transfer

7. Composite Floor Systems — UK Deck Profiles

The dominant UK floor solution is composite metal decking with shear studs. The deck acts as permanent formwork during construction and as external reinforcement for the composite slab in the final condition.

The critical construction-stage check is the unpropped deck deflection under the wet concrete weight (typically 2.4 kN/m^2 for a 130 mm slab). The deck manufacturer's load/span tables give the maximum unpropped span for a given total slab depth and construction load.

8. Worked Example — 3-Bay UK Office Frame

Design Brief

• 3-bay by 3-bay office building, 4 storeys
• Bay size: 7.5 m x 7.5 m
• Storey height: 3.5 m (ground to first: 4.0 m)
• Floor construction: ComFlor 60 composite slab, 130 mm total, A193 mesh
• Steel grade: S355 to BS EN 10025-2
• Lateral stability: Vertical X-bracing in perimeter bays

Loading (per EN 1991-1-1 + UK NA)

Secondary Beam (B1) — 7.5 m span at 2.5 m centres

• Tributary width: 2.5 m
• UDL: w_Ed = 9.90 x 2.5 = 24.75 kN/m
• M_Ed = 24.75 x 7.5^2 / 8 = 174.0 kN.m
• V_Ed = 24.75 x 7.5 / 2 = 92.8 kN

From SCI P365 for S355 simply supported beams, unbraced top flange during construction but fully restrained by composite slab in final condition:

Try 305x165x40 UB (S355):

• M_c,Rd = 215 kN.m > 174.0 kN.m — OK (utilisation = 0.81)
• V_pl,Rd = 407 kN > 92.8 kN — OK
• Deflection under imposed load only (2.5 m x 3.0 = 7.5 kN/m):
  • delta = 5 x 7.5 x 7500^4 / (384 x 210,000 x 85.0 x 10^6) = 14.3 mm
  • L/delta = 7500/14.3 = 525 > 360 — OK, stiff enough for a composite floor with brittle finishes

Use 305x165x40 UB in S355.

Primary Beam (B2) — 7.5 m span, point loads from B1

B1 beams frame into B2 at 2.5 m centres. Two point loads at third points:

• P_Ed per B1 = 92.8 kN (end reaction)
• M_Ed = 92.8 x 2.5 = 232.0 kN.m

Try 457x191x67 UB (S355):

• M_c,Rd = 454 kN.m > 232.0 kN.m — OK (utilisation = 0.51)
• Shear and deflection OK by inspection

Note the utilisation is low. If this beam is repeated across all floors, consider dropping to 406x178x54 UB (M_c,Rd = 289 kN.m, utilisation = 0.80) for material economy.

Column (C1) — Ground floor, internal

Axial load from 4 floors, tributary area 7.5 x 3.75 = 28.1 m^2 per floor:

• G_k: (2.8 + 1.2) x 28.1 x 4 = 450 kN (slab)
• Self-weight of steel: ~30 kN (beams + column)
• Q_k: 3.0 x 28.1 x 4 x 0.7 (reduction for 4 storeys per UK NA) = 236 kN
• N_Ed = 1.35 x (450 + 30) + 1.5 x 236 = 648 + 354 = 1,002 kN

Try 203x203x52 UC (S355), effective length 3.5 m (braced frame, pinned-pinned):

• N_b,Rd from P365 = 1,250 kN > 1,002 kN — OK (utilisation = 0.80)
• Check: The 152x152x37 UC would give N_b,Rd = 780 kN, insufficient.

Use 203x203x52 UC in S355.

Bracing Check

Design wind load per EN 1991-1-4, wind zone for Manchester:

• q_p = 0.93 kN/m^2 (basic velocity pressure, terrain category II, 14 m building height)
• Total wind force per storey = 0.93 x 7.5 x 3.5 x 1.3 (C_pe + C_pi) = 31.7 kN
• Brace force in X-brace at 45 degrees: F_brace = 31.7 x 1.414 / 2 = 22.4 kN (tension only)

Use M20 Macalloy 460 tension rod:

• T_Rd = A_s x f_y / gamma_M0 = 245 x 460 / 1.0 = 112.7 kN > 22.4 kN — OK

9. Typical UK Detailing Dimensions

10. Key Takeaways

1. Simple construction is the UK default for steel frames up to 10 storeys. It assumes pinned beam-to-column connections with lateral stability provided separately.
2. SCI P365 is the definitive UK design data source, tabulating pre-calculated member resistances for all standard sections in S275 and S355 per EN 1993-1-1 with UK National Annex.
3. Flexible end plates (partial-depth) are the dominant UK connection type, offering the best balance of fabrication economy and erection speed, with standardised designs to SCI P358.
4. UK column splices are typically 600 mm above floor level with flange cover plates transferring 50-60% of axial load per flange per SCI P207.
5. Composite metal deck floors with shear studs are the UK standard, using ComFlor (Tata Steel) or Multideck (Kingspan) profiles at 60 or 80 mm depth, with unpropped span limits dictated by the wet concrete construction stage.

PRELIMINARY — NOT FOR CONSTRUCTION. All design information is for educational reference only. Member sizing must be independently verified by a Chartered Structural Engineer (MIStructE or MICE) registered with the Engineering Council before use in any building project. Always check the latest National Annex, SCI guidance, and project-specific loading requirements.