Fin Plate Connection Design Calculator

What it checks

A fin plate (shear tab) is a simple beam-to-column or beam-to-beam shear connection: a plate welded to the supporting member and bolted to the supported beam web. This calculator verifies every failure mode EN 1993-1-8 requires and reports the governing one - bolt group in shear including the eccentricity effect, bolt bearing on both the plate and the beam web, the fin plate in gross shear, net shear, block tearing and bending, the beam web in shear and its interaction, the weld to the support, and punching shear of the supporting flange.

Fin plates are nominally pinned but the bolt line sits at an eccentricity from the support face, so the bolt group carries a moment as well as the shear. That eccentricity is what makes a fin plate check more involved than a simple bolt-capacity lookup, and it is the reason the bolt group so often governs.

Which mode governs, and why it is usually the bolts

Running the tool against the published Design Guide example gives the following resistances, and the pattern is typical of real fin plates:

Bolt group in shear (with eccentricity)

172.4 kN - GOVERNS

Bolt group in bearing

214.7 kN

Beam web, shear interaction

327.2 kN

Fin plate in bending

464.7 kN

Fin plate, block tearing

508.9 kN

Fin plate, net shear

565.8 kN

Fin plate, gross shear

581.0 kN

Supporting member, local shear

796.9 kN

The bolt group at 172.4 kN governs, and it is barely a third of the plate resistances. The single-bolt shear capacity is 94.1 kN, but the group of bolts does not give a simple multiple of that: the eccentricity reduction factor comes out at 0.51, roughly halving the group efficiency. That factor is the whole reason a fin plate is sized by its bolts.

The practical consequence is that adding plate thickness rarely helps a failing fin plate. Adding a bolt row, or reducing the eccentricity by moving the bolt line closer to the support, is what moves the governing number.

Detailing that the checks depend on

A fin plate only behaves as a pin if it can rotate. The plate must be short enough and the bolt group compact enough that the connection sheds moment rather than attracting it, and the tool classifies the plate as short or long because a long fin plate has an additional lateral-torsional check that a short one does not.

End and edge distances drive the bearing and block tearing resistances directly - the tool takes e1 and e2 on both the plate and the beam web, and the smaller of the two sets governs bearing. The supporting flange also needs a punching check: if the plate is thicker than the punching limit the weld can tear the flange out rather than the connection failing in a ductile mode.

Formula reference

Bolt shear per plane

$F_{v,Rd} = \dfrac{\alpha_v f_{ub} A_s}{\gamma_{M2}}$

Bolt group with eccentricity

$V_{Rd} = \dfrac{n\,F_{v,Rd}}{\sqrt{(1+\alpha n)^2 + (\beta n)^2}}$

Bearing

$F_{b,Rd} = \dfrac{k_1 \alpha_b f_u d t}{\gamma_{M2}}$

Plate gross shear

$V_{Rd,g} = \dfrac{h_p t_p}{1.27}\cdot\dfrac{f_y}{\sqrt3\,\gamma_{M0}}$

Plate net shear

$V_{Rd,n} = A_{v,net}\dfrac{f_u}{\sqrt3\,\gamma_{M2}}$

Block tearing

$V_{eff,Rd} = \dfrac{f_u A_{nt}}{2\gamma_{M2}} + \dfrac{f_y A_{nv}}{\sqrt3\,\gamma_{M0}}$

Punching limit on the support

$t_{p,\max} = \dfrac{f_{u,c}\,d}{1.5\,f_{u,p}}$

Assumptions and limits

The connection is treated as nominally pinned, carrying shear plus the moment from the bolt-line eccentricity. It is not a moment connection and this tool does not check rotational stiffness or classify the joint - if the frame analysis assumed a pinned joint, the detailing must allow the rotation the analysis implies.

The supporting member is assumed adequate in its own right: the tool checks local shear and punching of the supporting flange but not the column as a whole, nor web panel shear, nor stiffening. The supported beam is checked at the connection only, not for its own bending or lateral-torsional buckling.

Results are for a static persistent design situation with non-preloaded bolts in normal clearance holes. Fatigue, fire, seismic detailing and slip-critical categories are outside the scope.

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