Column Splice Types per EN 1993-1-8

End Plate Splice

Two columns with pre-welded end plates are bolted together with bolts passing through both plates. The end plates are typically 20-50 mm thick and project beyond the column flanges to accommodate the bolt circle. This type is common in UK and Irish practice for H-section columns up to approximately 350 mm depth.

Division Plate Splice

A single thick plate (division plate) is sandwiched between the upper and lower column ends. Flange cover plates transfer the flange forces, and web cover plates transfer shear. This type is preferred in continental European practice and for heavier columns where end plate splices become impractical.

Design Forces at a Column Splice

EN 1993-1-8 Clause 6.2.7.1 requires the splice to resist the following design actions:

1. Axial compression N_Ed — transferred through bearing and bolts
2. Major-axis moment M_y,Ed — transferred as a tension-compression couple through the flanges
3. Minor-axis moment M_z,Ed — transferred through flange bolts and web bolts
4. Shear V_Ed — transferred through the web splice or direct bearing of end plates

For typical braced frames, the splice is located at approximately mid-storey height (point of contraflexure for minor-axis buckling), which minimises the moment demand. A minimum eccentricity moment of N_Ed × h/200 should be considered per EN 1993-1-1 Clause 5.3.2(3) unless a more rigorous second-order analysis is performed.

End Plate Splice — Design Procedure

Flange Force Distribution

The flange forces in an end plate splice under combined compression and moment are:

N_f,Ed = (N_Ed / 2) + (M_y,Ed / (h_c − t_f))

Where the upper sign applies to the compression flange (compression increases) and the lower sign to the tension flange (compression reduces, may become tension).

Compression Flange Check

The compression flange transfers force through direct bearing of the end plates. EN 1993-1-8 Clause 6.2.7.1(4) allows the axial compression to be transferred entirely through bearing provided the contact surfaces are prepared (machined or close-sawn) and the bolts are tightened to at least snug-tight condition. No bolt slip is detrimental to this load path.

Bearing stress at the flange interface: σ_b,Ed = N_f,Ed / (b_f × t_f) ≤ f_y / γ_M0

Tension Flange Check (if applicable)

If the moment is large enough to produce net tension in one flange, the bolts must transfer that tension. The tension flange force is resisted by the bolts in the tension zone acting through the end plates in a T-stub configuration (Clause 6.2.4).

F_t,Ed = max(0, |(N_Ed / 2) − (M_y,Ed / (h_c − t_f))|)

Bolt Check per Flange Side

For end plate splices with n_bolt bolts per flange side:

• Shear: V_Ed,bolt = (N_f,Ed + T_f) / n_bolt (where T_f is any required preload)
• Bearing: F_b,Rd per EN 1993-1-8 Table 3.4
• Combined: (F_v,Ed / F_v,Rd)² + (F_t,Ed / F_t,Rd)² ≤ 1.0 (if tension present)

Division Plate Splice — Design Procedure

Flange Cover Plate Capacity

Flange cover plates transfer the flange axial force between the upper and lower column sections:

A_cover ≥ N_f,Ed / (f_y / γ_M0)

Typical cover plate thickness: t_cover ≥ max(0.5 × t_f, 15 mm)

Cover plate bolt group: designed per EN 1993-1-8 Clause 3.6 for the full flange force.

Longitudinal spacing: 4d_0 minimum, 14t_min or 200 mm maximum (EN 1993-1-8 Table 3.3).

Division Plate Bearing

The division plate transfers the total column axial compression. Bearing check per EN 1993-1-8 Clause 6.2.7.1(5):

σ_c,Ed = N_Ed / A_division ≤ f_y / γ_M0

Division plate thickness should be at least 1.5 × t_f (column flange thickness) to ensure adequate load distribution into the column section beyond.

Worked Example — HEB 260 End Plate Splice

Step 1 — Flange Forces

Flange force from compression + moment couple: Lever arm: z = h_c − t_f = 260 − 17.5 = 242.5 mm

Compression flange: N_f,c = 1,850/2 + 65/0.2425 = 925 + 268 = 1,193 kN Tension flange: N_f,t = 1,850/2 − 65/0.2425 = 925 − 268 = 657 kN

Both flanges remain in compression — no net tension.

Step 2 — End Plate Bearing Check

Flange interface bearing (machined surface): σ_b = 1,193,000 / (260 × 17.5) = 1,193,000 / 4,550 = 262.2 MPa

Allowable bearing: f_y / γ_M0 = 355 / 1.00 = 355 MPa Utilisation = 262.2 / 355 = 0.739 — OK for machined bearing

Step 3 — Bolt Shear Check (Construction Phase)

During erection before full bearing develops, bolts carry the self-weight of the upper column length (assumed 3.5 m storey height, HEB 260 mass = 93 kg/m):

Erection shear per bolt: V_Ed,erect = (93 × 3.5 × 9.81 / 1000) / 8 = 3.19 / 8 = 0.40 kN — negligible

Post-construction, horizontal shear V_Ed = 45 kN transferred through end plate friction: Friction force = N_Ed × μ = 1,850 × 0.30 = 555 kN >> 45 kN — OK

Step 4 — Bolt Design for Robustness

Even though bolts are not structurally required for compression transfer, they must satisfy robustness requirements. Check 8 × M24 Class 8.8 bolts in double shear through 2 × 35 mm end plates:

Single shear per bolt plane: F_v,Rd = 0.6 × 800 × 353 / 1.25 = 135.6 kN Double shear (two planes): F_v,Rd,total = 2 × 135.6 = 271.1 kN per bolt

Total shear capacity = 8 × 271.1 = 2,169 kN > 1,850 kN — OK

The bolt capacity exceeds the column squash load, providing adequate robustness should bearing be lost (e.g., during a fire or impact scenario).

Splice Location Guidelines

The splice should also respect practical constraints: column sections are typically delivered in lengths up to 12-15 m (articulated lorry) or 18 m (extendable trailer). The splice location must allow safe access for the steel erector — typically at least 600 mm above the finished floor level to provide working space for bolt tightening.

Frequently Asked Questions

What is the difference between an end plate splice and a division plate splice? An end plate splice uses two end plates (one pre-welded to each column end) bolted together face-to-face. This is a compact, shop-welded solution ideal for lighter columns (HEB 160-320 range) and provides direct bearing for compression transfer. A division plate splice uses a single thick plate sandwiched between column ends, with separate flange and web cover plates bolted across the splice. This is preferred for heavy columns (HEB 300 and above), seismic-resisting frames where ductile behaviour is required, and where site adjustment of column length is necessary. Division plate splices provide better tolerance for fabrication errors because the division plate can be machined to exact thickness.

How are column splices checked for combined compression and moment? EN 1993-1-8 Clause 6.2.7.1 requires the splice to resist the full design actions at splice level. The flange forces are calculated from the elastic section properties: N_f = N_Ed × (A_f / A) ± M_y,Ed / (h_c − t_f). The compression flange force is transferred through bearing (machined surfaces), while any tension must be carried by bolts through the end plate or cover plate in bending. The web carries its proportional share of axial force plus any shear. For braced frames where the splice is at the point of contraflexure, the moment is typically small and the splice is compression-dominated. For unbraced frames or splice locations away from inflection points, the moment component becomes significant and may require tension capacity in the flange bolts.

What are the erection stability requirements for column splices? EN 1993-1-8 Clause 6.2.7.1(6) requires the splice to have adequate strength and stiffness during erection, before the full connection is made and before the concrete slab provides lateral restraint. The splice must resist the self-weight of the upper column and any temporary construction loads (typically 1.0 kN/m² over the tributary area). At least 25% of the bolts must be in position and snug-tight before the crane hook is released. For bolted end plate splices, this means at least 2 bolts per flange. For cover plate splices, at least one bolt per cover plate. Temporary erection angles or cleats are often used to locate the upper column and provide stability while bolts are installed.

How are splice bolts checked for slip resistance in Category C connections? For Category C slip-resistant connections per EN 1993-1-8 Clause 3.4.2, the splice bolts must be preloaded (to EN 14399 or EN 1090-2) and checked for slip resistance at the serviceability limit state (SLS) in addition to bearing at ULS. The slip resistance per bolt is F_s,Rd = k_s × n_s × μ × F_p,C / γ_M3, where k_s accounts for hole type (1.0 for normal holes), n_s is the number of friction interfaces (2 for a cover plate with bolts in double shear), μ is the slip factor (0.30 for surfaces blasted to SA 2.5, 0.40 for surfaces blasted and painted with frictional coating), and F_p,C is the preload force (247 kN for M24 8.8 per EN 14399). For splices where slip would be detrimental (e.g., moment-resisting frames with tight drift limits), Category C is specified. For most column splices in simple construction, Category A (bearing type) is sufficient.

Design Resources

• EN 1993 Column Design — Buckling per EN 1993-1-1
• EN 1993 End Plate Connection Design
• EN 1993 Bolt Group Capacity — Eccentric Load
• EN 1993 Bolt Bearing and Tearout — Clause 3.6
• EN 1993 Steel Grade Properties — f_y and f_u
• European Steel Beam Sizes — IPE, HEA, HEB
• All European Reference Guides

Reference only. Verify all values against the current edition of EN 1993-1-8:2005 Clause 6.2.7 and the applicable National Annex. Design calculations must be independently verified by a licensed Structural Engineer. This guide is for educational purposes only and does not constitute professional engineering advice.