Is this a do-able moment connection?
Is this a do-able moment connection?
(OP)
I'm trying to make a moment connection between two HSS members. They're radiused but we won't worry about that for now.
Welding isn't an option and the achitect is pushing hard for a clean looking connection.
I came up with an idea that is shown in the attached sketch. Is this even possible? Am I asking for nightmarish istallation headaches?
Any advice would be appreciated.
P.S. I know this would be a highly uneconomical connection.
Thanks,
Adam
Welding isn't an option and the achitect is pushing hard for a clean looking connection.
I came up with an idea that is shown in the attached sketch. Is this even possible? Am I asking for nightmarish istallation headaches?
Any advice would be appreciated.
P.S. I know this would be a highly uneconomical connection.
Thanks,
Adam






RE: Is this a do-able moment connection?
Well I don't know what load your putting on but I wouldn't want to be any where near it,
It looks like your sliding a flat bar into a box section if my understanding is correct and if thats the case I have a question:- How do you weld something thats labelled 10mm ring 200mm down inside another box section?
desertfox
RE: Is this a do-able moment connection?
I am having a hard time trying to see what is going on here.
RE: Is this a do-able moment connection?
If the pieces do not fit snugly together (which is usually the case with HSS) you would need to provide packing pieces to ensure a snug fit.
BA
RE: Is this a do-able moment connection?
Stillerz: the sektch is of a moment connection between two HSS members. More specifically, it connects the two halves of a steel arch rib member that must be split for shipping and galvanizing.
BA: In my detail, I was using the single bolt to take up slack in the connection for serviceability purposes. Theres some other hardware that would prevent axial seperation of the HSS segments. What exactly are these packing pieces? Have you used that method before?
RE: Is this a do-able moment connection?
Are these "ring plates" in the shape of something similar to a block "O"?
How do you intend to weld the "ring plate" inside the HSS?
RE: Is this a do-able moment connection?
He doesn't intend to weld them on the inside he is going to split the box, I asked the same question, doesn't look a very good idea to me
desertfox
RE: Is this a do-able moment connection?
Yeah, the original had an HSS inside piece. I may go back to that once I get a chance to crunch some numbers. The ring plates would basiscally look like stiffeners or cap plates with 102 x 152 penetrations cut out of them so that the inner tube could pass through.
As I mentioned above, the ring stiffeners would break the HSS. The HSS on either side of the ring stiffners would be prepped with an angular cut and full or partial penetration welded. No welding inside the HSS.
Adam
RE: Is this a do-able moment connection?
I guess the porblem with it is, it isn't really a connection. The only thing holding it together is a set screw and some compression forces (i'm assuming)
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
They spliced HSS to HSS with a smaller piece of HSS inside and through bolts on either side. Where the main pieces of HSS butted on the outside, they must have been milled. The butt joint was almost invisable.
The problem is findig a piece of HSS to fit snugly inside the large a BS said.
I thought it was a very nice looking connection.
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
I have used a very similar type connection but with much larger sections where it was easier to get the welds done on the inside.
Another option is to have two cross bolts in sleeves to take the moment.
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
No, I haven't done that type of connection before and I would have concerns about fitting them together in the field. Very difficult with a snug fit. The outside member is 203 x 152 (8" x 6")outside. You don't give us the thickness. If it is 6.4 (1/4") the inside dimension is 7.5" x 5.5". A 7" x 5" member fits in easily but has too much play. The packing pieces would be, say 1/4" flats bent around the corners and welded to the inner tube, one at each end of the lap. When inserted into the outer tube, this would fit nice and snug.
You could even skip the end plate on the right hand member in your sketch and let the insert HSS extend both ways from the splice. I would certainly want to discuss such a detail with the fabricator before going too far with it because it will be a pain to erect.
BA
RE: Is this a do-able moment connection?
The thickness of the HSS isn't yet determined. I'm pretty keen on the packing piece idea though -- that's slick. I'll run it by some fabricators here and see if that might be the answer.
Kootenay
RE: Is this a do-able moment connection?
Can you give me a little more detail about the cross bolt idea? It sounds interesting Is it one sleave on top of the HSS and one on the bottom, both running parallel to the HSS? Is this essentially a prestressed connection?
KK
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
Sleeve is through the inside tube but unfortunately you cannot fully tension the bolts as it may crush in the outer tube walls.
RE: Is this a do-able moment connection?
You said that the pieces were galvanized. Hence, before shipping but after galvanizing (which will affect clearance).
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
Well my concerns are alignment after welding as the parts are bound to distort, I have no idea what load your putting on this except that its the centre of a arch how do you know the joint is strong enough.
Looking at the plate section sliding into the larger box section with the clearence between the two,the rings that support the flat plate become point load supports that will transer all the load from one box section to the other with very little bearing area.
This in turn will transfer the load to the 8mm fillet weld on the righthand side of your joint which means there's a bending moment on the fillet weld as well as shear and at the far side of the joint where you split the box into two to put a stiffening ring in again your relying on the totally on the weld.
How confident are you that the load transferred in the joint won't just rest on one edge of a single stiffening ring and the rest carried the bottom of the adjusting screw because you will never get those 2 support rings perfectly level, which from the sketch is what is required.
What are you going to do during welding as the box sections are galvanised, which after welding they certainly won't be galvanised anymore and I am fairly confident that attempting to weld galvanised steel gives off toxic fumes.
I think what BAretired is suggesting is sound in that by packing all round the joint so its snug it will transfer the load from one to the other over a much larger bearing area then your drawing suggests.
hope this helps
desertfox
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
Alignment after welding is a good point. I was planning to have the assembly galvanized after all of the welding is performed. With no closed sections, I had hoped that this would be possible.
I intended to use the set screw only to keep the thing snug under service loads. In an ultimate case, I'm positive that the inner tube would be resting on one edge of each ring as you described. The connection would have to be designed to work exactly that way.
As for the rest, you've basically described the precise load path that I had in mind. The loads are small which works in my favor. Everything that you've pointed out would certainly have to be checked.
Based on the advice provided in this thread, I am hoping to go with something more practical and less dubious analytically. We'll see what my architect thinks...
RE: Is this a do-able moment connection?
Is this the idea??
KK
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
I wonder if you could manage it as a slip critical connection for light loads? If that were the case, maybe I could use an oversized hole with a plate washer.
RE: Is this a do-able moment connection?
Thats a much better idea provided its strong enough to take the loads.
desertfox
RE: Is this a do-able moment connection?
-Why isn't welding an option? It would be super easy to make a slick connection. Maybe you already said and I missed it.
-What about a bolted end flange with stiffeners. It wouldn't be invisible, but sometimes architects like them.
RE: Is this a do-able moment connection?
Welding is out because we'd have to metalize or otherwise touch up the galvanizing after welding. These aren't really exposed to the elements so the architect questions how well the galvanizing and touch up will blend. Basically, we don't want the touch up work to be apparent.
Yeah, I tried to sell a bolted end plate moment connection too. No...such...luck.
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?
If the sleeve is thick enough, you could drill and tap it to receive the alignment/keeper bolts, or you could use a rivet nut/Nutsert or similar to allow one sided bolting. That would keep clean lines to, of course, satisfy the architect.
I have used this approach in aluminum structures and it works well.
RE: Is this a do-able moment connection?
The attached page shows a typical sleeve connection for HSS members for cantilevered sign posts which take moment. The sketch seems similar to what you are trying to accomplish. It is from a book called Engineering Sign Structures by Benjamin Jones. I've never designed one so I can't be much help other than background info.
RE: Is this a do-able moment connection?
No, I do not work or worked for CWMM or 4DEng. I just happened to be living in Kelowna at the time I joined the forum and it was as good a username as any other.
RE: Is this a do-able moment connection?
i'd use 4, two on the sides (as shown), 2 on the top and btm faces, interpitched.
and this is going to look neater than retouched weldments ?? CSK bolts no doubt.
RE: Is this a do-able moment connection?
sigh
RE: Is this a do-able moment connection?
If loads permit, I would try to sell the attached connection to the architect.
RE: Is this a do-able moment connection?
RE: Is this a do-able moment connection?