Bolted beam-to-beam connections using hollow sections are not that common – more often than not, where these connections occur, it’s usually found to be an open section beam connecting to a hollow section supporting beam. However, there will always be instances where you may come across them.
Here, we’ll look at a few connection options which include connecting two hollow sections and connecting open section beams to a hollow section – these include using both Through and Blind Fasteners.
Connections with end-plates or cleats are very much the same – using end-plates will generally provide a neater, more compact connection allowing for the use of through or blind fasteners. The end plate may be full, covering the end of the section, or cut as a flange which can ‘slip over’ the beam end thus leaving the end open – which is a more costly option.
If the sections are to be galvanized after fabrication - then leaving the ends open is obviously advantageous, but the profile will not be sealed against the ingress of moisture and debris for the life of the structure.
Closing the ends, will not allow the zinc to penetrate the inside surfaces – so normal practice is to allow for holes to be drilled through the end-plate to allow for the ingress of the molten zinc and the expulsion of gasses.
(Galvanizing and the preparation of steelwork will be covered in a later post)
Typical Connections using Hollow Section Beams
Bolting a hollow section beam to another is not something you'll see very often, but they do occur - so here's a few suggestions on how they might be done:
Fig. 1 illustrates a cleat / end-plate connection where the cleat is shop-welded to the top of the supporting beam while the incoming beam is fitted with an end-plate. The top connects to the cleat using Through Bolts, while the bottom is Blind Bolted to the side face of the supporting beam.
Fig. 2 shows an angle cleat connection where the end-plate on the incoming beam is substituted with a cleat - the means of fastening the connection is the same as before. Here the incoming beam end may be left open (as per Fig. 2) or closed using a closure plate (Fig. 3)
Another option is to weld a Tee-stub (Fig. 4) to the supporting beam, the same size as the incoming beam, which is fitted with an all-round flange. The length of the stub should be such as to allow for the insertion and tightening of the bolts.
It's worth noting here, the bolt pattern, where it's not recommended to place the bolts beyond the outside faces of the incoming beam.
For more about this and further information on recommended bolt spacing and edge-distances, go to: Bolt Spacing
Using Circular Hollow Sections
Using a circular hollow section beam usually implies that the beam is simply a Tie, which means the connecting beam need not align the top flange with that of the supporting beam. There are a few option here - the most common arrangement is to weld a Tee-stub to the sidewall of the supporting beam (Fig. 5), usually at the center with a flange extending far enough to insert and tighten the bolts.
Alternatively, the stub may be extended to fully pass through the supporting beam (Fig. 6) which may then be closed with a closure plate. This will provide a much stronger connection and will offer greater resistance to tension and compression, but it comes at a price - this is very time-consuming and costly and should only be used where absolutely necessary under instruction from the responsible engineer.
The flanges may be either circular or square. As you would expect, a circular flange would be more costly, while a square flange uses less material, is easier to fabricate and depending on how you see these things, looks better.
The bolt holes for all circular hollow sections are always set out according to the PCD (Pitch Circle Diameter) while the edge distances are in accordance with standard practice.
For more information on this, go to: Bolt Spacing
Connecting Open Section Beams to a Hollow Section
Of all the options available, this is probably the most widely used when considering end-plates. having said that, end-plates are not usually the first choice - though they provide a neater, more compact solution - they are usually substituted by the Fin-Plate, which offers a more cost-effective alternative, which is straightforward to fabricate and far easier to erect. having said that - here are a few suggestions:
Fig, 7 illustrates two variations - the first is to fit the end plate to the incoming beam end and bolt directly to the supporting beam using Blind Fasteners. Alternatively, you could weld a Tee stub protruding far enough to insert and tighten the bolts and connect to the incoming beam using Through Fasteners.
Using open sections, the end-plate will be smaller in line with normal end-plate standards covering the 3 options of using a Partial (as illustrated) or an extended or full-depth end-plate.
For more information on standard end-plates go to: Welded End-Plates