From members to joints. This lesson follows a beam's end shear through a bolted fin plate into the column: bolts in shear and bearing, the eccentric bolt group, the plate, the beam web and the welds, to SANS 10162-1, by hand and in the STATIX fin plate calculator.
1. Learning outcomes
After this lesson you can:
explain how a fin plate carries shear and why it counts as a simple connection;
find a bolt's shear and bearing resistance and choose a bolt grade;
find the force on the worst bolt of an eccentric group;
check the plate, the beam web, block failure and the welds, and the detailing distances;
check a fin plate in the STATIX fin plate calculator.
A fin plate connection: a plate welded to the column (or a primary beam) and bolted to the web of the beam. It carries the beam's end shear and lets the end rotate a little, so the beam acts as simply supported.The load path. The beam's end shear goes from its web into the bolts, from the bolts into the plate, through the welds into the column. The connection is as strong as its weakest link, and the calculator reports which one it is.
4. One bolt: shear and bearing
Bolt shear (SANS 10162-1, 13.12.1.2). The bolt is cut across where the two plates slide. Threads in that plane leave less steel, hence the 0.70. φb = 0.80; fu of the bolt: 400 (4.6), 420 (4.8), 500 (5.6), 830 (8.8), 1 040 MPa (10.9).Bolt grades. The first number is roughly the ultimate strength in hundreds of MPa; the second the yield ratio. 8.8 is the usual structural bolt. A stronger bolt only helps while the bolt itself governs: bearing on a thin web does not change.Bearing (SANS 10162-1, 13.10(c)). The bolt presses on the side of its hole. A thin plate crushes there; a bolt close to an edge tears a plug out. a is the distance from the hole centre to the edge in the direction it would tear; STATIX uses the smaller of the end and edge distances. φbr = 0.67; fu is the plate's.
shear, per plane: Vr = 0.60 φb Ab fu × 0.70 (threads in), φb = 0.80
bearing, per bolt: Br = min(3 φbr t d fu, φbr a t fu), φbr = 0.67
the bolt's resistance = the smaller of its shear and the bearing on the plate and on the web
5. The bolt group
The bolt group (elastic vector method). The shear arrives at the face of the support, a distance e from the bolts, so the group also carries a moment V e. Each bolt gets V/n plus a part of the moment in proportion to its distance from the centre. SANS has no bolt-group clause of its own; STATIX declares this method.
per kN of V on the corner bolt: down 1/n (+ e x / Σr²), across e y / Σr²
k = the resultant; Vr,group = (bolt resistance) / k
6. The plate, the beam web and the welds
The plate itself: shear on its full depth, and bending at the bolt line as a short cantilever from the weld. A plate no thicker than half the bolt diameter (SCI P358; there is no SANS clause) yields first, which gives the joint the rotation a simple connection needs.Block failure (SANS 10162-1, 13.11). A block of plate or web can tear out along the bolt holes: shear along the line, tension across. STATIX checks the plate and the beam web; a notched beam end uses the reduced 13.11 b) form. Net areas deduct each hole at its size + 2 mm, and punched holes 2 mm more again.The welds to the support (SANS 10162-1, 13.13.2.2). Two fillet welds along the plate carry the shear and the moment from the eccentricity. A fillet loaded across its length is stronger than one loaded along it, which the angle term allows for.
7. Detailing
Detailing (SANS 10162-1, 22.3). Bolts need room: at least 2.7 d apart, and far enough from ends and edges (Table 8, by bolt size and edge type) so the plate does not split. STATIX checks every distance and shows it against its limit.
8. In STATIX
The STATIX fin plate calculator: choose the supported beam and the plate, the bolts (size, grade, rows, one or two columns), the pitch, gauge and edge distances, the shear and what the plate is welded to. It draws the joint to scale and lists every component with its clause.
9. Example A: a one-line fin plate
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10. Example B: two bolt lines for a bigger reaction
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11. Do it in STATIX
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12. Common mistakes
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13. Exercises
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14. Self-check quiz
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15. Lesson 5 on one page
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Next: Lesson 6, welded connectionsFillet welds, weld groups and end plates. Go to lesson 6
A worked example for learning, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.
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