Beam Splice Types per EN 1993-1-8

Bolted Flange Plate Splice

Flange forces are transferred through cover plates bolted to the top and bottom flanges of the connected beam sections. The web splice uses separate cover plates (one each side) to transfer shear. This is the standard field splice in European practice — it does not require welding on site, is faster to erect, and is easier to inspect.

Welded Beam Splice (Shop Only)

Full-penetration butt welds at the flange and web — used when the splice is fabricated in the workshop and transported as a single piece. Not recommended for field splices due to access, weather, and inspection constraints. Per EN 1993-1-8 Clause 4.7, butt welds must achieve full penetration with backing bars or back-gouging.

Design Forces at a Beam Splice

EN 1993-1-8 Clause 6.2 requires the splice to develop the forces at the splice location from the governing load combination:

1. Bending moment M_y,Ed — transferred as a tension-compression couple through the flange cover plates
2. Shear V_Ed — transferred through the web cover plates and their bolt groups
3. Axial force N_Ed (if present) — shared between flanges and web in proportion to their areas

For simply supported beams, splices are ideally positioned at approximately one-quarter span to minimise the design moment. For continuous beams, splices at points of contraflexure minimise both moment and flange force demands.

Bolted Flange Plate Splice — Design Procedure

Flange Force Determination

The flange force at the splice under moment M_y,Ed:

F_f,Ed = M_y,Ed / (h_b − t_f)

Where h_b is the beam depth and t_f is the flange thickness. The lever arm (h_b − t_f) is the distance between flange centroids.

For pure bending (no axial force), the top flange is in compression and the bottom flange is in tension (or vice versa depending on the sign convention). Each flange cover plate is designed for its respective force direction.

Flange Cover Plate Sizing

The cover plate cross-sectional area must equal or exceed the beam flange area:

A_cover ≥ A_f = b_f × t_f

Cover plate width should match the beam flange width where possible. Minimum thickness:

t_cover ≥ max(0.5 × t_f, 12 mm)

Per EN 1993-1-8 Clause 3.3, the plate steel grade should match or exceed the beam steel grade. For S355 beams, use S355 plates.

Bolt Group Design per Flange Side

Each side of the splice requires a bolt group to transfer the flange force from the beam flange into the cover plate. Bolts are loaded in single shear (flange + cover plate interface).

Number of bolts required: n ≥ F_f,Ed / F_v,Rd

Where F_v,Rd is the design shear resistance per bolt per EN 1993-1-8 Table 3.4:

F_v,Rd = (α_v × f_ub × A) / γ_M2

For Class 8.8 bolts with threads in the shear plane: α_v = 0.6, γ_M2 = 1.25.

Bolt Spacing and Edge Distances

Per EN 1993-1-8 Table 3.3:

• Minimum pitch: 2.2 d_0 (centre-to-centre along force direction)
• Minimum edge distance: 1.2 d_0 (in force direction)
• Maximum pitch (compression): 14 t_min or 200 mm
• Maximum edge distance: 12 t or 150 mm

Where d_0 is the bolt hole diameter (typically d + 2 mm for M20 and above).

Net Section Check

The cover plate net section at the first bolt row (closest to the splice centreline) must be verified:

N_net,Rd = (0.9 × A_net × f_u) / γ_M2 ≥ F_f,Ed

Where A_net = t_cover × (b_cover − n_h × d_0), with n_h being the number of bolt holes in the critical cross-section.

Web Plate Splice — Shear Transfer

The web splice transfers the design shear V_Ed through web cover plates (one or both sides of the web).

Bolt Design for Web Splice

Web splice bolts are typically in double shear (two shear planes: beam web to each cover plate). For M20 Class 8.8 bolts in double shear:

F_v,Rd = 2 × (0.6 × 800 × 245) / 1.25 = 2 × 94.1 = 188.2 kN per bolt

Number of bolts required: n ≥ V_Ed / F_v,Rd_per_bolt

Web Cover Plate Thickness

Per good practice, each web cover plate should be at least 0.5 × t_w in thickness. When two plates are used (one each side), the combined shear area should equal or exceed the beam web area:

2 × h_cover × t_cover ≥ h_w × t_w

Minimum practical thickness: 6 mm for carbon steel plates per EN 1993-1-1.

Bearing Check on Web Plates

Per EN 1993-1-8 Table 3.4, the bearing resistance per bolt:

F_b,Rd = (k_1 × α_b × f_u × d × t) / γ_M2

Where α_b accounts for end distance and bolt spacing, and k_1 accounts for edge distance perpendicular to the load direction.

Worked Example — IPE 450 Beam Splice

Step 1 — Flange Force

Lever arm: z = h_b − t_f = 450 − 14.6 = 435.4 mm

F_f,Ed = 520 × 10^6 / 435.4 = 1,194 kN per flange

Step 2 — Flange Cover Plate Check

Flange area: A_f = 190 × 14.6 = 2,774 mm^2 Cover plate area: A_cover = 190 × 22 = 4,180 mm^2 > 2,774 mm^2 — OK

Tension capacity of cover plate: N_pl,Rd = A_cover × f_y / γ_M0 = 4,180 × 355 / 1.00 = 1,484 kN > 1,194 kN — OK

Step 3 — Flange Bolt Group Design

M24 Class 8.8, threads in shear plane: A = 353 mm^2 F_v,Rd = 0.6 × 800 × 353 / 1.25 = 135.6 kN per bolt per shear plane

Single shear (one plane): bolts required = 1,194 / 135.6 = 8.8 → use 12 bolts per flange per side (2 rows × 6)

Alternatively, with threads excluded from the shear plane: F_v,Rd = 0.6 × 800 × 452 / 1.25 = 173.6 kN. Required = 1,194 / 173.6 = 6.9 → use 8 bolts. Check grip length to ensure the unthreaded shank crosses the shear plane.

Step 4 — Net Section Check

Cover plate: 22 mm thick, 190 mm wide. Two holes per row (d_0 = 26 mm for M24): A_net = 22 × (190 − 2 × 26) = 22 × 138 = 3,036 mm^2

N_net,Rd = 0.9 × 3,036 × 490 / 1.25 = 1,071 kN per plate

Flange force per plate (top or bottom): 596.5 kN per side < 1,071 kN — OK

Step 5 — Web Splice Design

V_Ed = 210 kN. M20 Class 8.8 in double shear: F_v,Rd = 188.2 kN per bolt.

Bolts required = 210 / 188.2 = 1.1 → use 6 bolts (3 per side, 2 columns × 1 or 2 rows). Minimum 2 bolts per side per EN 1993-1-8 recommendation for erection stability.

Step 6 — Bearing Check on 8 mm Web Cover Plate (M20 bolt, e_1 = 35 mm)

α_b = min(e_1 / (3 d_0), p_1 / (3 d_0) − 0.25, f_ub / f_u, 1.0)

α_b = min(35 / (3 × 22), 70 / (3 × 22) − 0.25, 800 / 490, 1.0) = min(0.53, 0.81, 1.63, 1.0) = 0.53

k_1 = min(2.8 × e_2 / d_0 − 1.7, 2.5) = min(2.8 × 35 / 22 − 1.7, 2.5) = min(2.75, 2.5) = 2.5

F_b,Rd = 2.5 × 0.53 × 490 × 20 × 8 / 1.25 = 83.1 kN per bolt < F_v,Rd = 94.1 kN (single shear equivalent) — bearing governs.

Total bearing capacity = 6 × 83.1 = 498.6 kN > V_Ed = 210 kN — OK

Splice Location Guidelines

Splice location should also consider crane lifting capacity during erection. A 15 m IPE 450 section weighs approximately 1.2 tonnes — within the capacity of most mobile cranes on commercial building sites.

Frequently Asked Questions

When should a beam splice be designed as slip-resistant (Category B or C)?

Per EN 1993-1-8 Clause 3.4, slip-resistant connections are required when: (1) slip would cause a serviceability issue (Category B, SLS check); (2) the connection is subject to load reversal or impact (Category C, ULS check); (3) fatigue loading is present; or (4) the splice is in a hybrid or composite girder where slip would redistribute internal forces. For standard simply supported beams with static gravity loads, Category A (bearing type) is adequate.

How are flange cover plate bolts checked for combined shear and bearing?

Each bolt in the flange cover plate group must satisfy two checks: (1) shear — F_v,Ed ≤ F_v,Rd per EN 1993-1-8 Table 3.4; and (2) bearing on the connected plies — F_b,Ed ≤ F_b,Rd for the thinner ply (cover plate or beam flange). The bearing check is performed with the actual bolt configuration (end distance, edge distance, pitch). The governing check is typically bearing on the cover plate when the cover plate is thinner than the beam flange, or shear in the bolt when the bolt is the limiting component.

What is the difference between a bearing splice and a slip-resistant splice per EN 1993-1-8?

A bearing splice (Category A) transfers load through bolt bearing on plate material — the bolts are loaded in shear and the plates in bearing. Some slip occurs as clearance holes engage. A slip-resistant splice (Categories B and C) uses preloaded bolts (to EN 14399) with controlled surface preparation to develop friction at the faying surfaces. Category B checks slip at SLS with γ_M3,ser = 1.10; Category C checks slip at ULS with γ_M3 = 1.25. Category C is the most demanding and costs more due to bolt preloading and surface preparation requirements.

What bolt spacing rules apply to beam splice cover plates per EN 1993-1-8 Table 3.3?

Minimum bolt pitch is 2.2 d_0 (centre-to-centre along the force). Minimum edge distance is 1.2 d_0 (force direction) and 1.5 d_0 (perpendicular). Maximum pitch is min(14 t_min, 200 mm) for compression and min(14 t_min, 200 mm) for tension (exterior), where t_min is the thinner connected ply. Maximum edge distance is 12 t or 150 mm for corrosion protection. For M24 bolts (d_0 = 26 mm), the minimum pitch is 57.2 mm and minimum end distance is 31.2 mm — use 60 mm and 35 mm respectively.

Design Resources

• EN 1993 Beam Design — Flexure and Shear per EN 1993-1-1
• EN 1993 End Plate Connection Design
• EN 1993 Bolt Group Capacity — Eccentric Load per Clause 3.6
• EN 1993 Bolt Bearing and Tearout — Table 3.4
• EN 1993 Column Splice Design — Clause 6.2.7
• EN 1993 Steel Grades — f_y and f_u Values
• All European Reference Guides →

Reference only. Verify all values against the current edition of EN 1993-1-8:2005 Clause 6.2 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.