HSS beam to HSS column welded connection 1

[conradlovejoy]

I've always tried to avoid detailing a tube beam welded to the face of the two supporting columns because I feel like this creates a difficult tolerance window and constructability issue. Even if the steel is manufactured perfectly, field installation of the columns could create a situation where the beam is slightly too long to fit (a situation in which I guess it could be shaved in the field), or worse, too short such that there is a gap that is too large to adequately weld one end. I don't know off hand what the tolerance for gaps between two pieces of weld metal is, but I imagine it could be such that a field bust that doesn't create a structural stability issue could still make a proper weld impossible.

Can someone with more wisdom and experience than I let me know if I am avoiding this very easy detail unnecessarily or if my concerns are legitimate?

 

[r13]

Minimize field fitting and welding is the correct choice.

 

[gtaw]

If you have a seat (with a stiffener) connection for the tube to sit on, and a top plate if there is moment to contend with, it is doable. It wouldn't be at the top of my list for favorable connections. The question is, how do you make the connection during erection and secure it until it is welded?

An alternative is end plates on the tubular beam and clips on the tubular column face. There would be no field welding and if the beam is too short to plumb the structure, shim plates would have to be used. It would be necessary to verify the beams were not too long during fabrication.

Where there is a need, tube to tube connections can be accommodated, but they can be troublesome.

Best regards - Al

 

[CANPRO]

HSS to HSS can be a pain. Is this for a specific connection or a general question? If it’s just simple shear you have lots of options for a bolted connection. If it’s a moment connection it can get trickier.

The other big consideration is the architectural space. If it’s 6” tubes hidden in a 6” wall you might have some trouble...if you can extend connection material beyond the profile of the tubes then you gain a lot more options for bolted connections.

 

[conradlovejoy]

It's just a general question. I see other engineers detail this connection when they want to make a moment connection between tube beam and columns and I feel its just because its really easy to draw that detail. In the real world, trying to get that situation to fit, especially if its tens of times, seems like a recipe for errors.

Thanks for the responses so far. I feel a bit more justified in my concern.

 

[conradlovejoy]

gtaw, I've always imagined they set the beam in place with crappy temporary welds until they are ready to do the real welding. I'm not sure, which always makes me feel like I shouldn't be detailing it that way then.

 

[r13]

Isn't the beam seat gets in place prior to beam erection, if so provided. For fitting direct weld connection, the welder will provide temporary taps to hold the beam steady in position. A lot of weld metal will be wasted if there is a gap.

 

[CANPRO]

For installing a field welded HSS beam you'd have a temporary erection seat or some sort of tab and erection bolt - this allows you to set the location of the beam before lifting it in place and allows you to to release the crane (if applicable) and move on to other work while the connection is welded out.

If you're confident in your surveyor and the schedule allows for it, you can survey the beam location and cut to suit in the shop. Alternatively you can send the HSS to site 1" long and trim to suit. You might be able to close small gaps with come alongs between columns (as long as column stays within tolerance).

Field welded HSS is the worst option by far. Try to bolt any chance you can. I did a solo brainstorming session and sketched out a few bolted connections - I drew these details assuming the beam and column has the same width. I got lazy on the weld details, but you get the intent. Details labelled for further discussion if you'd like.

 

[phamENG]

I like F with a vertical plate bolted to a single plate shear tab coming off of the column. The most common application I've had for this kind of thing is headers for ribbon windows. Most of the time we just detailed it similar to A because everything else gets in the way of the window. The modified F could be adjusted so the connection stays above the bottom (for a head) or top (for a sill) of the HSS and still work.

 

[BAretired]

At one point, I was retained by a fabricator to design connections. One project involved a large vierendeel truss using HSS sections for chords and web members. The chords were 10x10HSS, the web members were 8x8HSS. The wall thickness was 1/2" for all truss members. The documents specified full strength welds throughout. The architect wanted the clean appearance of HSS members neatly welded together and ground smooth, with no external plates exposed to view.

I requested the design forces and moments from the EOR as it was not possible to provide full strength welds, but he declined, insisting upon enforcing the contract documents. My client ended up cutting the chords at every panel point, welding double stiffeners to align with the walls of every web member and welding it all back together again.

My client was not a happy camper.

BA