Connection Components

A fin plate connection consists of:

1. Fin plate — Steel plate welded to the supporting member (column or beam), bolted to the beam web
2. Bolts — 2-5 bolts in a single vertical line through the beam web
3. Welds — Fillet weld connecting fin plate to support (both sides)
4. Beam web — The beam web is the thinnest plate and often governs bolt bearing

Typical Geometry

Design Checks — EN 1993-1-8

1. Bolt Shear Resistance

F_v,Rd = 0.6 × f_ub × A_s / γ_M2

For M20 8.8 (A_s = 245 mm²): F_v,Rd = 0.6 × 800 × 245 / 1.25 = 94.1 kN per bolt

2. Bolt Bearing (Beam Web)

F_b,Rd = (k₁ × α_b × f_u × d × t_w) / γ_M2

For IPE 300 (t_w = 7.1 mm), M20, S355: k₁ = min(2.8×35/22 - 1.7, 2.5) = 2.50 α_b = min(35/(3×22), 800/470, 1.0) = 0.53 F_b,Rd = (2.50 × 0.53 × 470 × 20 × 7.1) / 1.25 = 70.7 kN per bolt

3. Fin Plate in Bearing

Same formula with t = 10 mm (plate thickness): F_b,Rd = (2.50 × 0.53 × 470 × 20 × 10) / 1.25 = 99.6 kN per bolt

The beam web bearing governs at 70.7 kN per bolt.

4. Fin Plate in Bending

M_pl,Rd = t_p² × h / 4 × f_y / γ_M0

For 200×90×10 plate in S355: M_pl,Rd = 10² × 200 / 4 × 355 / 1.00 = 17.75 kN·m

5. Fin Plate Shear (Gross Section)

V_pl,Rd = h × t_p × (f_y / √3) / γ_M0

For 200×10 plate: V_pl,Rd = 200 × 10 × 205 / 1.00 = 410 kN

6. Fin Plate Shear (Net Section)

V_net,Rd = (h - n × d₀) × t_p × (f_u / √3) / γ_M2

For 3×M20 (d₀ = 22 mm): V_net,Rd = (200 - 3×22) × 10 × 271 / 1.25 = 290 kN

7. Block Shear

Per EN 1993-1-8 Clause 3.10.2, check block shear on both fin plate and beam web. Block shear typically governs for thin beam webs.

Weld Design

Fillet weld connecting fin plate to support:

Capacity Table — Fin Plate in S355

Note: Beam web bearing (t_w) governs in all cases. Increase beam web thickness or use higher grade bolts to increase capacity.

Frequently Asked Questions

What checks are required for fin plate connection design per EN 1993-1-8?

The seven checks are: (1) bolt shear, (2) bolt bearing on beam web, (3) bolt bearing on fin plate, (4) fin plate in bending (due to eccentricity from beam web centreline), (5) fin plate gross shear, (6) fin plate net shear at bolt holes, (7) block shear on fin plate and beam web. The weld to the support and the support member itself must also be verified.

Why does the beam web bearing govern in fin plate connections?

The beam web is typically the thinnest element in the connection (IPE 300 t_w = 7.1 mm vs fin plate t_p = 10 mm). Since bearing resistance is proportional to the plate thickness, the beam web gives the lowest F_b,Rd. Where higher capacity is needed, options include thicker beams, additional bolts (longer fin plate), or higher bolt grade.

Related Pages

• End Plate Connection — Moment connection per EN 1993-1-8
• Gusset Plate — Brace connection design
• Brace Connection — Brace per EN 1993-1-8
• Bolt Bearing — Bearing per Clause 3.6
• All European References

Educational reference only. Design per EN 1993-1-8:2005. Fin plate design methodology per SCI/BCSA Green Book P358. Verify beam web thickness and eccentricity moment. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

Worked Example -- Fin Plate Connection (EN 1993-1-8)

Problem: Design a fin plate (shear tab) connection for a simply-supported secondary beam IPE 300 in S275 steel to a primary beam web. Design shear force V_Ed = 120 kN.

Given:

• Secondary beam: IPE 300, S275 (Fy = 275 MPa, Fu = 430 MPa)
• Fin plate: S275, tp = 10 mm, bp = 160 mm, hp = 280 mm
• Bolts: 4 M20 Grade 8.8 (2 columns x 2 rows), pitch = 70 mm, gage = 80 mm
• Bolt holes: 22 mm dia. (standard clearance for M20)
• Edge distance e1 = 40 mm vertical, e2 = 40 mm horizontal

Solution:

Step 1 -- Bolt shear resistance (EN 1993-1-8 Table 3.4):

alpha_v = 0.6 (shear plane through unthreaded portion assumed)
Fv,Rd = alpha_v * fub * As / gamma_M2
      = 0.6 * 800 * 245 / 1.25
      = 117,600 N = 94.1 kN per bolt (single shear)

Total = 4 * 94.1 = 376.4 kN > 120 kN  OK

Step 2 -- Bolt bearing on fin plate (EN 1993-1-8 Table 3.4):

e1 = 40 mm > 1.2*d0 = 1.2*22 = 26.4 mm  OK
alpha_d = e1 / (3*d0) = 40 / 66 = 0.606

For end bolts: alpha_b = min(alpha_d, fub/fu, 1.0) = min(0.606, 800/430, 1.0) = 0.606

k1 = min(2.8*e2/d0 - 1.7, 2.5) = min(2.8*40/22 - 1.7, 2.5) = min(3.39, 2.5) = 2.5

Fb,Rd = k1 * alpha_b * fu * d * tp / gamma_M2
      = 2.5 * 0.606 * 430 * 20 * 10 / 1.25
      = 2.5 * 0.606 * 430 * 200 / 1.25
      = 104,232 N = 104.2 kN per bolt

Step 3 -- Fin plate shear (gross section, EN 1993-1-1 6.2.6):

Vpl,Rd = Av * Fy / (sqrt(3) * gamma_M0)
       = (280 * 10) * 275 / (1.732 * 1.0)
       = 2800 * 158.8
       = 444,640 N = 444.6 kN > 120 kN  OK

Step 4 -- Beam web bearing check (primary beam web tp = 10 mm, S275):

Fb,Rd per bolt = 2.5 * 0.606 * 430 * 20 * 10 / 1.25 = 104.2 kN (same geometry)
Total bearing = 4 * 104.2 = 416.8 kN > 120 kN  OK

Result: Fin plate 280 x 160 x 10 mm with 4 M20 Grade 8.8 bolts, fillet welded to primary beam web (6 mm FW both sides), is adequate for V_Ed = 120 kN. DCR = 120/376.4 = 0.32 (bolt shear governs nominally but fin plate shear is the ductile mechanism).

EN 1993-1-8 Clause References for Shear Tab Design

• EN 1993-1-8 Section 3.6 -- Bolts, nuts, and washers specified for shear connections
• EN 1993-1-8 Table 3.4 -- Design resistance of individual fasteners (shear, bearing, tension)
• EN 1993-1-8 Section 3.10 -- Long joints and reduction for connections over 500 mm
• EN 1993-1-8 Section 4.5.3.2 -- Fillet weld design resistance (directional method)
• EN 1993-1-1 Section 6.2.6 -- Shear resistance of cross-sections for plate checks
• EN 1993-1-1 Section 6.2.5 -- Block tearing (block shear) check for fin plate

Design Resources

Calculator tools

• Bolted Connection Calculator
• Weld Capacity Calculator
• End Plate Moment Connection Calculator
• Fin Plate Shear Connection Calculator
• Gusset Plate Calculator

Design guides

• Bolted Connection Worked Example
• Bolted Connection Checklist
• Steel Connection Calculator Guide
• Weld Design Checklist
• EN 1993-1-8 Bolted Connection Worked Example

Reference pages

• EU Shear Tab
• UK Moment Connection