Simple Connection Types — EN 1993-1-8 Clause 5.2

A nominally pinned connection transmits shear without developing significant moments. Three types dominate UK/European practice:

Bolt Group Shear — EN 1993-1-8 Table 3.4

For a bolt group with n bolts, the design shear resistance per bolt:

F_v,Rd = alpha_v × f_ub × A / gamma_M2

Where alpha_v = 0.6 for Grade 8.8 (shear plane passes through threads), 0.5 for Grade 4.6 or 5.6.

For M20 Grade 8.8 (A_s = 245 mm², gamma_M2 = 1.25): F_v,Rd = 0.6 × 800 × 245 / 1.25 = 94.1 kN per shear plane.

For a 6-bolt fin plate (single shear, 3 rows × 1 column): V_Rd,bolts = 6 × 94.1 = 564.6 kN. However, the bolt group may be governed by the furthest bolt in the group under combined shear and torsion.

Bolt Bearing — EN 1993-1-8 Table 3.4

For a fin plate (S275, t = 10 mm) with M20 bolts:

F_b,Rd = k1 × alpha_b × f_u × d × t / gamma_M2

Where:

• alpha_b = min(e1/3d0, p1/3d0 - 1/4, f_ub/f_u, 1.0)
• k1 = min(2.8e2/d0 - 1.7, 1.4p2/d0 - 1.7, 2.5)
• e1 = end distance = 40 mm, e2 = edge distance = 35 mm, d0 = 22 mm (hole)
• p1 = 70 mm (bolt pitch)

alpha_b = min(40/(3×22), 70/(3×22)-0.25, 800/410, 1.0) = min(0.606, 0.811, 1.951, 1.0) = 0.606. k1 = min(2.8×35/22-1.7, 1.4×70/22-1.7, 2.5) = min(2.75, 2.75, 2.5) = 2.5.

F_b,Rd = 2.5 × 0.606 × 410 × 20 × 10 / 1.25 = 99.4 kN per bolt.

Block Tearing — EN 1993-1-8 Clause 3.10.2

For a fin plate with bolt group at the supported beam web:

V_eff,Rd = f_u × A_nt / gamma_M2 + f_y × A_nv / (sqrt(3) × gamma_M0)

For a 230 × 100 × 10 mm fin plate with 3 M20 bolts at 70 mm pitch, 40 mm end distance: A_nv = (40 + 2×70) × 10 = 180 × 10 = 1800 mm² (net shear area). A_nt = (35 + 35 - 22) × 10 = 480 mm² (net tension area).

V_eff,Rd = 410 × 480 / 1.25 + 275 × 1800 / (1.732 × 1.00) / 1000 = 157.4 + 285.8 = 443.2 kN.

Worked Example — Beam-to-Column Fin Plate

Problem: UK beam 356x171x45 UB (S355) connecting to 203x203x52 UC column (S355). Design shear V_Ed = 160 kN. Design a fin plate connection.

Step 1 — Fin Plate Sizing:

Plate: 230 × 100 × 10 mm, S275. Welded to column flange with 6 mm fillet weld. Bolts: 3 rows × 1 column M20 Grade 8.8, 22 mm clearance holes, 70 mm pitch, 40 mm end/edge.

Step 2 — Bolt Shear Check:

F_v,Rd per bolt (single shear, threaded in shear plane) = 94.1 kN. Total V_Rd = 3 × 94.1 = 282.3 kN > 160 kN. OK (57% utilisation).

Step 3 — Bolt Bearing on Fin Plate:

F_b,Rd = 99.4 kN per bolt (from above). Total V_Rd = 3 × 99.4 = 298.2 kN > 160 kN. OK.

Step 4 — Bolt Bearing on Beam Web (t_w = 6.9 mm):

alpha_b = min(40/(3×22), 0.811, 800/470, 1.0) = 0.606 (same as fin plate). k1 = 2.5 (through-part, no edge effect).

F_b,Rd = 2.5 × 0.606 × 470 × 20 × 6.9 / 1.25 = 78.6 kN. Total V_Rd = 3 × 78.6 = 235.8 kN. Governed by beam web bearing. Still > 160 kN. OK.

Step 5 — Block Tearing of Beam Web:

A_nv = (40 + 2 × 70) × 6.9 = 1242 mm². A_nt = (35 - 11) × 6.9 = 166 mm².

V_eff,Rd = 470 × 166 / 1.25 + 355 × 1242 / (1.732 × 1.00) / 1000 = 62.4 + 254.6 = 317.0 kN > 160 kN. OK.

Selected: 230×100×10 mm fin plate S275, 6 mm FW, 3-M20 Gr 8.8 bolts at 70 mm pitch.

Tying Resistance � EN 1991-1-7 Structural Integrity

UK Building Regulations Approved Document A (Structure) requires that all buildings of Class 2B and above have structural ties to resist disproportionate collapse. EN 1991-1-7 Annex A specifies a tying force per connection:

• Internal ties: T_i = max(0.8 � (g_k + psi � q_k) � s � L, 75 kN) where s = tie spacing, L = span.
• Peripheral ties: T_p = max(0.4 � (g_k + psi � q_k) � s � L, 75 kN).

For an 8 m beam span at 3.5 m centres with g_k = 3.5 kPa and q_k = 4.0 kPa (psi = 0.5 for offices): T_i = max(0.8 � (3.5 + 0.5 � 4.0) � 3.5 � 8.0, 75) = max(0.8 � 5.5 � 3.5 � 8.0, 75) = max(123.2, 75) = 123.2 kN.

The fin plate connection must be verified for tying: check bolt group tension, fin plate tension (net section), supporting column web tension, and weld to supporting member. For the worked example with 3-M20 Grade 8.8 bolts:

Bolt tension in tying: F_t,Rd per bolt = k_2 � f_ub � A_s / gamma_M2 = 0.9 � 800 � 245 / 1.25 = 141.1 kN. Total tying capacity = 3 � 141.1 = 423.3 kN > 123.2 kN. OK.

Fin plate net section in tension: A_net = (b - n � d_0) � t = (100 - 3 � 22) � 10 = 340 mm� (conservative). N_Rd = 0.9 � A_net � f_u / gamma_M2 = 0.9 � 340 � 410 / 1.25 / 1000 = 100.4 kN. This is less than 123.2 kN � the fin plate net section governs over the bolts.

To satisfy tying, increase plate to 120 mm wide: A_net = (120 - 3 � 22) � 10 = 540 mm�. N_Rd = 0.9 � 540 � 410 / 1.25 / 1000 = 159.4 kN > 123.2 kN. OK.

Tying resistance often governs UK connection design for robustness Class 2B buildings (5+ storeys or >2000 m� floor area). The fin plate width, bolt size, and weld size may all require uprating.

Double Angle Web Cleat Connections

Double angle cleats (two angles bolted to the beam web, legs bolted to the supporting member) are a traditional UK simple connection. Per SCI P358:

Cleat sizing: Angle leg size typically 90�90�8 mm or 100�100�10 mm for beams up to 610 mm deep. Bolts in one or two vertical columns through the outstanding legs into the supporting member.

Bolt group design: For a 100�100�10 angle cleat with 3-M20 Grade 8.8 bolts at 70 mm pitch:

• Beam web bolts (bearing through cleat + web): use the double-shear bolt capacity.
• Supporting member bolts (bearing through cleat only): single shear.

Rotation capacity: The outstanding leg of the angle acts as a flexible element allowing end rotation of the simply supported beam. The critical check is the block tearing of the angle leg under the bolt group.

For a 100�100�10 angle in S275, with 3-M20 bolts at 50 mm end distance, 35 mm edge: A_nv = (50 + 2 � 70) � 10 = 1900 mm�. A_nt = (35 - 11) � 10 = 240 mm�.

V_eff,Rd = 410 � 240 / 1.25 + 275 � 1900 / (1.732 � 1.00) / 1000 = 78.7 + 301.7 = 380.4 kN per cleat.

Total for two cleats: 2 � 380.4 = 760.8 kN, typically exceeding the bolt shear capacity. The bolts govern.

Design tip: Double angle cleats provide excellent tying resistance because the two angles effectively double the net section. They are preferred when tying is critical and the fin plate net section proves insufficient.

Related Pages

• EN 1993 Connection Design — Eurocode Overview
• EN 1993 Moment Connection — Bolted End Plate
• EN 1993 Bolt Capacity — Bolt Tables
• EN 1993 Bolt Hole Sizes — Clearances
• EN 1993 Weld Sizes — Minimum Fillet Welds
• EN 1993 CHS Connection — Hollow Section Joints
• UK Fin Plate Connection — SCI P358 Green Book
• Bolted Connection Calculator — Free Tool

Educational reference only. Simple connection design per EN 1993-1-8:2005 and SCI P358. Verify against current Eurocodes and UK National Annex. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent Chartered Engineer verification.