Fin plate connection design to SANS 10162-1
A 356 × 171 × 45 beam on a 230 × 100 × 10 fin plate with three M20 class 8.8 bolts, carrying 150 kN: the eccentric bolt group, bolt shear and bearing, plate shear, block failure and bending, the beam web and the fillet weld. Every number below comes from the free STATIX fin plate calculator and was checked by hand.
1. The problem
| Input | Value |
|---|---|
| Supported beam | 356 × 171 × 45 I-section, web tw = 6.9 mm, S355 |
| Fin plate | 230 × 100 × 10 mm, S355 (fy 355, fu 470 MPa), welded to a column flange |
| Bolts | 3 × M20 class 8.8 in one vertical line, pitch 70 mm, end distance 45 mm, 50 mm from the bolt line to the beam end |
| Gap | 10 mm between the beam end and the support face |
| Weld | 8 mm fillet both sides of the plate |
| Design load (factored) | end shear V = 150 kN, no axial force |
SANS 10162-1 has rules for almost every part of a fin plate: bolts (13.12), bearing (13.10), block failure (13.11), plate shear (13.4) and bending (13.5), and welds (13.13). Resistance factors: φ = 0,90 (steel), φb = 0,80 (bolts), φbr = 0,67 (bearing), φw = 0,67 (weld metal).
2. Eccentricity and the bolt group
The shear enters at the support face and the bolts sit 60 mm away (gap 10 + 50 mm). That eccentricity puts a moment on the bolt group. SANS 10162-1 has no clause for it; the elastic method is used, as is common practice:
Σr² = 70² + 0 + 70² = 9 800 mm² (bolts at −70, 0, +70 mm)
direct shear per bolt Fv = 150 / 3 = 50,0 kN
moment share at the end bolt Fm = M rmax / Σr² = 9 000 × 70 / 9 800 = 64,3 kN
resultant Fb = √(50,0² + 64,3²) = 81,4 kN
3. Bolt shear (cl. 13.12.1.2)
The 0,70 applies when the threads are in the shear plane, the usual case for a fin plate. fu = 830 MPa for class 8.8 (13.12.1.2 NOTE).
4. Bolt bearing (cl. 13.10(c))
Bearing on each ply is the lower of 3φbr t d fu and φbr a t fu, where a is the end distance:
beam web (t 6,9, a 45 mm): 97,8 kN
The bolt group resistance per bolt is the lowest of shear and bearing: 87,6 kN (bolt shear). Check: 81,4 ≤ 87,6 kN (93%). This governs the connection.
5. The fin plate
block failure (13.11 a): 435,7 kN (34%)
bending (13.5): Mr = φ Ze fy, Ze = tp hp²/6 = 88 167 mm³ → Mr = 28,2 kNm ≥ 9,0 kNm (32%)
6. The beam web
block failure (13.11 a): 329,8 kN (45%)
7. The weld (cl. 13.13.2.2)
The two 8 mm fillets carry the shear and the moment. Per millimetre of weld the resultant is 606 N/mm, at an angle of 57° to the weld axis, so the strength increase for a transverse load applies:
8. Result
| Check | Result |
|---|---|
| Bolt group, 13.12.1.2 / 13.10(c) | 81,4 ≤ 87,6 kN (93%), governs |
| Fin plate shear, 13.4.2 | 150 ≤ 485 kN (31%) |
| Fin plate block failure, 13.11 | 150 ≤ 436 kN (34%) |
| Fin plate bending, 13.5 | 9,0 ≤ 28,2 kNm (32%) |
| Beam web shear and block failure | 45% |
| Weld, 13.13.2.2 | 606 ≤ 1 688 N/mm (36%) |
The connection works at 93%, governed by the end bolt. A fourth bolt (or a second bolt line) brings the moment share down quickly, because Σr² grows with the square of the bolt spacing.
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