Hollow Section to Hollow Section
Fin-Plate connections are relatively straightforward to detail and fabricate and offer many advantages over End-Plates, chief among them is that they allow for Through Bolts. There are 3 common options for making such connections as indicated in Fig’s. 1, 2 and 3 below.
The most common is illustrated in Fig. 1 where the fin-plate is welded to the outside face of the supporting beam while the incoming beam is closed off with a Tee section, match-drilled to suit the fin-plate. The Tee may be either a standard hot-rolled Tee profile or fabricated from plates. There should be a 10 mm gap between the end of the plate and the face of the connecting profiles – this will allow sufficient clearance for the welds. This connection is used for lightly loaded connections.
A stronger connection is illustrated in Fig. 2 where a Tongue plate is introduced to replace the Tee. The Tongue plate in inserted into the incoming beam at a depth not less than the width of the profile. (This is an arbitrary rule-of-thumb which should be confirmed by the responsible engineer) The end of the beam may be left open or closed using closure plates which are welded to the beam end abutting the tongue plate, this being the more widely used option.
For small member sizes, welding the plate inside the profile may prove problematic, in which case the option shown in Fig. 3 may be considered.
This option is similar to the previous except the tongue plate protrudes from the top and bottom of the profile allowing it to be welded from the outside. To achieve this, slots must be cut into the incoming beam to a depth equalling the intrusion of the plate. As with option 2, the incoming beam end may be left open or sealed with closure plates.
Connecting an Open Section Beam to a Hollow Section.
In just about every case this is the more widely used application – connecting an open section beam to a hollow section is simple and straightforward. The fin-plate may be welded to the outside of the supporting hollow section, as shown in Fig. 4, or for a much stronger connection, the fin--plate may be inserted through slots cut into the beam and fully welded. This second option, shown in Fig. 5, is however costly and time consuming and should only be used under the direction of the responsible engineer.
Setting out the Connection
Generally, when connecting two hollow section beams, the drill pattern of the fin-plate is set out equally about the center of the incoming beam. If the incoming beam is an open section, the drill pattern is set out from the top flange in accordance with standard practice.
This is not a ‘hard and fast’ rule but another recommendation toward Standardization.
For more information on setting-out fin-plates for open section beams go to Welded Fin-Plates