Slotted tube Connection_brace

[Veer007]

Hey guys, i have a situation where my detailer slotted the tube column at base plate due to its larger brace force, however it seems to be wrong as far as i know, has anyone encounter a same situation?

Thanks in advance!!

 

[KootK]

Mousework. So far, I hate drawing on screens. It's unfortunate as I'm usually an early adopter with that kind of thing.

 

[JLNJ]

Not all detailing offices have engineers. Many hire out the PE stamping only if it is an explicit requirement.

Is this a delegated-design? Who is actually designing the connection? The OP makes it sound like the detailer has simply drawn it this way and is asking the OP to "approve" of it.

Looking at the weld stress from the plate to the brace, the length of weld might be the critical element. Maybe the designer intends for there to be weld inside and out of the tube. It's only 5" deep, so 20" total length. If the tube is big enough, maybe they can reach inside. On the column, that's a lot of weld, even though it's just one-sided.

The real question is "Who is responsible for the design?" and "What is the intent?"

 

[r13]

The EOR is responsible to review and stamp the submittal, either "Approved", "Approved with noted", "Revise and resubmit", or "Reject". The intent of delegate design work to other entity is to save time and money by utilizing a dedicate source for works considered cumbersome, and free up own engineering personnel to perform more productive works. This usually occurs at projects of considerable size, and handled by large companies. Although the final responsibility (permit-wise) falls on the shoulder of the EOR, the companies will have legal contract to assign liability shall something falls apart. I wouldn't doubt there are cases with rubber stamp, but important is the design turns out. If one does not want to see future works, you can be as sloppy as you wish and not get paid.

 

[hokie66]

I for one, in my 40 some years of practice, never delegated connection design. But whether or not you do, as EOR you are still responsible for the connections. If one fails, guess who is in the firing line.

Now back to the connection at hand. human909 tried (4 Jan 15:19) to make the point above that out of plane eccentricity of the plates must be considered, and I agree with him that the 1/2" gussets are probably too thin.

 

[JLNJ]

I don't think we know the jurisdiction, but under the AISC Code of Standard Practice you have three options: (1) provide the complete design as part of the original design documents, (2) let the detailer choose the connections through experience and from published documents/tables, or (3) provide the loads and completely delegate the design.

My question was not so much to the point of whether or not the EOR has ultimate responsibility (they likely do) but a more practical one. If the connections have been delegated, have the connection engineer submit the calcs as to what his intent is (for the welds in question).

This connection probably falls outside the realm of detailer work (option 2) and into the realm of engineering work. Exactly who does what gets a little squirrely and that's why AISC devotes 2+ pages of commentary in the code for the three options. I'm just curious which option the OP selected for his project.

 

[human909]

Veer007 has yet to return to this thread. Hopefully he is busy with something interesting and will come back. Who is responsible for what is and interesting game and discussion, but any good engineer should look past a poor design.** Veer007 has ask the question so he clearly is in some position of responsibility regarding this connection.

Slotting in of itself is not a problem, in fact it is often a very good solution. The issue though whether the plate has the capacity to convey the forces in the bracing. The brace seems to be a 10" HSS. Unless it is over-designed or quite long then that would imply significant forces for the connection the handle. For connections like this I'm often doing 1"-1.25" plate to satisfy compression loads and eccentricities.


**I wish the world was this ideal. Sadly I see inadequate design more frequently than I would like. You can't join every battle particularly if you have not direct contractual relationship with the other parties and they have more letters after their signature... :-(

 

[JAE]

I agree with the points made by hokie66, human909, and JLNJ above about delegation and the relative thin gusset plate.

One other point - most gusset/brace connections tie into a column so as to fully integrate the column overall stiffness (think gussets aligned with WF webs or at least stiffened webs).
Here, we have a gusset extending through a wall, or rather a pair of walls, of a tube such that I can perceive a much higher tube wall flexibility compared with the base plate.
Perhaps so much that the majority of the brace force only flows though the base and essentially ignores the column as the walls of the tube deflect. That would be a big factor in how you check this connection.

KootK - not sure why a pair of channels would make any difference to how the weld symbol is portrayed. The channels above the gusset would have to be welded together as well somehow.
The fillet weld symbol problem would still be a problem - and now you'd be welding, or trying to build, a fillet onto a curved flange tip on the inside as well.

 

[KootK]

...and now you'd be welding, or trying to build, a fillet onto a curved flange tip on the inside as well.

I was envisioning flanges out rather than flanges in with the difference being whether or not your weld symbol would be traversing a hollow or one solid plate element of a flanged part (channel). I was gunning for a salient example with the weld symbol business rather than trying to make a robust column.

 

[r13]

I did work on both types of delegation. At company one, we only indicate support/joint reactions on the drawing (graphically and tables), then the "detailer" design the connections. I did review the design, and acted on it for the EOR, but I don't recall seeing the calculations, but it must be part of the contract document in permit package. At company two, we design the connections, and have the "detailer" to develop construction drawings.

I mentioned the delegation only to remind people who don't aware the role of "detailers", they are/can be engineers just like you and I, though the name doesn't reflect the professional level they actually in.

 

[JAE]

With back-to-back channels, KootK, I think the original double weld symbol would be OK as you would be welding on opposite sides of a contact plane, similar to the detail you posted.

 

[r13]

Veer007,

If you have any doubt on design done by the detailer, ask him/her to submit proof (usually design calculation, including code provisions) for review. He/she shall comply as you/your company owns the design.

 

[KootK]

...welding on opposite sides of a contact plane...

That suggests an attractive definition: other side = opposite side of the contiguous steel contact plane.

 

[hokie66]

This paper has been referenced in this forum before, but here it is again. This failure condition is what some of us have been warning against with the thin plates.

http://ascjournal.com/down/vol6no2/vol6no2_2.pdf

And this:

https://www.steel.org.au/resources/...rically-loaded-bracing-clea/download-pdf.pdf/

 

[JAE]

KootK - exactly.

 

[r13]

Sorry for getting back to the concern of "delegation". Just find something interesting to share.

Delegated Connection Design
When performing connection design that has been delegated by the engineer of record (EOR), we sometimes receive contract documents that do not appear to comply with the building code. We seem to have two choices: We could strictly follow the requirements as shown in the contract documents, or we could redesign the connections to meet the building code. Doing the latter may be stepping on the EOR’s toes and would be detrimental to our client, the fabricator, as the details would likely be more expensive than those shown in the contract documents. Can you provide any advice?

There are really two issues: your responsibility as a licensed engineer and your responsibility to your client as it relates to your and their contractual obligations

The full text can be viewed through the link Link

 

[Veer007]

Guys, i'm agreeing the weld symbol is wrong, will change as per your advise...

I'm the checker who works for a fabricator, my detailer team has a licensed engineer who is responsible for all connection but also need approval from an EOR.

Guys i too familiar with blue beam software, its really good...

Except the buckling stress of gusset, the connection is good as i think. This one make sense...Can i add a 1/2" stiffener to gusset to reduce its buckling, will this work?

Veer007 has yet to return to this thread.

Hey dude, i'm here..





Thanks in advance!!

 

[hokie66]

Stiffeners can be used in lieu of using thicker plates.

 

[phamENG]

If you have access to AISC documents, I would recommend Design Guide 29 - Vertical Bracing Connections. Even if your jurisdiction doesn't follow AISC, it is a valuable resource for understanding gusset behavior and items to consider in design.

 

[jayrod12]

Is adding gussets really cheaper than providing an appropriate thickness plate?

So you need 3/4" plate instead of 1/2" plate. Adding gussets adds pieces and welding. Seems foolish to me. But I don't do connection design.

 

[phamENG]

I know field welding is often considered taboo, but since this is a brace connection I would imagine those bolts will be slip critical so you'll either need specialized fasteners or specialized testing already to verify installation AND surface prep requirements for the matting surfaces. If you weld it, you can just enlarge the gusset a little and run it into the slot. Add a hole for an erection bolt, and then field weld it. That reduces the number of pieces and eliminates your eccentricity in the gusset which could reduce the size further.