Bolted connections

How a bolted fin plate is designed to EN 1993-1-8: bolt shear and bearing, end and edge distances, the eccentric bolt group, block tearing, and the plate and beam web, with the SCI P358 rules that the code leaves out, by hand and on the EN route of the STATIX fin plate calculator.

1. Learning outcomes

After this lesson you can:

trace the load path through a fin plate and list its checks;
work out the shear and bearing resistance of a bolt by Table 3.4, with α_v, α_b and k₁;
find the force on the worst bolt of an eccentric group;
check block tearing, the plate and the beam web;
check a fin plate in the STATIX fin plate calculator.

2. Before you start

Lesson 1 (net areas and block tearing) and the polar second moment of a group of points.
The free STATIX fin plate calculator, set to EN 1993-1-8.
A pocket calculator and about 55 minutes.
The same lesson on the SA code: Steel Design 1, lesson 5 (SANS 10162-1).

3. The fin plate and its load path

The fin plate. A plate is welded to the column or the supporting beam and the supported beam’s web is bolted to it. It is a simple (nominally pinned) connection: it carries the beam’s end shear, and rotates a little through the bolts and the plate.

The load path. The shear passes from the beam web into the bolts, from the bolts into the plate, through the plate and its weld into the support. Every link is checked; the weakest sets the connection resistance.

4. One bolt: shear and bearing

Bolt shear (EN 1993-1-8 Table 3.4). Each bolt is cut on one plane in a fin plate. Where the threads lie in the shear plane, the tensile stress area A_s counts, and the factor α_v depends on the bolt class. The calculator always takes the threads in the plane, on the safe side.

Bearing (Table 3.4). The bolt presses on the wall of its hole. The resistance falls when the bolt is close to an end in the direction of the load (α_b, from e₁/3d₀ or p₁/3d₀ − 1/4) or close to an edge across it (k₁). Bearing is checked on the plate and on the beam web.

F_v,Rd = α_v f_ub A_s / γ_M2 (Table 3.4) F_b,Rd = k₁ α_b f_u d t / γ_M2 α_b = min(α_d; f_ub/f_u; 1.0); α_d = e₁/3d₀ (end bolts) or p₁/3d₀ − 1/4 (inner bolts) k₁ = min(2.8 e₂/d₀ − 1.7; 1.4 p₂/d₀ − 1.7; 2.5) (edge bolts; inner bolts use the p₂ term)

End, edge and spacing (Table 3.3). e₁ and p₁ run in the direction of the load, e₂ and p₂ across it. Table 3.3 sets the minimum values (1.2 d₀ for ends and edges, 2.2 d₀ and 2.4 d₀ for the spacings) and maximum spacings; the calculator checks them first.

5. The bolt group

Eccentricity. The weld is at the face of the support, the bolts further out. For the bolts the shear acts at e = g + e_2b (plus half the gauge with two bolt columns) from the support face, so the bolt group carries V and a moment V e. The weld carries V and its own moment.

The bolt group (elastic vector method). The moment V e turns the group about its centre; each bolt resists in proportion to its distance from it. Adding that to the direct share V/n gives the resultant on each bolt; the corner bolt carries the most. EN 1993-1-8 gives no group method of its own: the calculator uses this one, as SCI P358 does, and says so.

Bearing at an angle. A corner bolt pushes down and sideways. Its end and edge distances are different in the two directions, so the calculator works out a vertical and a horizontal bearing resistance for each bolt and combines the two components, for the plate and for the beam web.

6. Block tearing, the plate and the beam web

Block tearing (3.10.2). The bolts can tear a block out of the plate or the beam web: shear down the bolt line, tension across to the edge. A fin plate is loaded eccentrically to the block, so the calculator uses equation (3.10) with half the tension term; with two bolt columns the tension plane crosses both.

The plate itself. It must carry the shear on its gross and its net section, the moment V e across its depth, and its weld (lesson 6). It must also be thin enough to bend and let the beam end rotate, so that the bolts are not overloaded: SCI P358’s ductility rule, which EN 1993-1-8 does not have.

What the fin plate calculator’s EN route uses: γ_M0 = 1.0 and γ_M2 = 1.25 (recommended); bolt f_ub 800 MPa for class 8.8 and 1 000 for 10.9, threads always in the shear plane; holes d₀ = d + 2 mm (d + 3 for M30); plate and web f_u by thickness from EN 1993-1-1 Table 3.1 (S355: 490 MPa up to 40 mm, 470 above); the elastic bolt group with bearing checked in both directions; block tearing by (3.10); plate bending with 6.2.8; the SCI P358 ductility rule t_p ≤ 0.5 d; and Table 3.3 for the layout. It also checks the supporting column flange or beam web, and notched beams.

7. In STATIX

The fin plate calculator’s EN route: choose the code “EN 1993-1-8 + SCI simple conn.”, the supported beam, the plate and the bolts with their layout, the design shear and the support; read every check and the weakest link.