Welded Gusset Connection
Welded Gusset Connection
(OP)
I'm using a slotted tube to gusset plate plate connection and the fabricator made the slots a bit wide - some of the slots are 3/4", which leaves 3/16" gaps on each side of the 3/8" gusset plate. The contractor is filling the gap with weld material, then adding the required filet over that, but, as I interpret AWS, he must oversize the filet by the size of the gap - i.e., a 5/16" weld must be upped to 1/2" (8/16") to achieve the proper effective size. It is my interpretation of AWS that this is too large a weld for 3/8" material, particularly when the filet goes on both sides of the gusset - only guidance I can find is a formula in AISC which states that the minimum plate thickness should be 5.16xD/Fy, but no specific code reference. Contractor's welder does not believe this is a problem. Any comments/suggestions would be appreciated.





RE: Welded Gusset Connection
Your tube would have a slight eccentricity so this would have to be reviewed, but it should work.
RE: Welded Gusset Connection
RE: Welded Gusset Connection
Another possibility, which is kind of what they're doing when they fill the gap with weld metal, is to make it a CJP or PJP groove weld. If what they've done already fits one of the prequalified joint geometries in D1.1, you're in luck.
Hg
RE: Welded Gusset Connection
Do yourself a favour though, clear it with the client and designer first. The insert bar might introduce new variables that were not considered by the design. I don't know if whatever you are building is a regulated item. If it is the inspection body might need to be involved too.
Good luck.
RE: Welded Gusset Connection
Unfortunately, the only solution would be to weld build-up the oversized gap along one slotted edge and trim as required to achieve the proper weld joint clearance. The weld build-up would provide material to adequately tie into, and result in only one fillet weld of the correct size. Since this is a scew-up, somone has to make this thing right regardless of cost to repair.
RE: Welded Gusset Connection
I don't believe from your description that the weld is oversized in the context that AWS is referring to as the extra weld is not on the tube being connected, it could be on the gusset however. All in all the fabricator is responsible for adequate pre-heating as well as inspection. If you have concerns about their procedures you can specify NDT testing of the weldment as well as the base metal to check that everything is acceptable.
If you have an opportunity please review the literature published by the Lincoln (Arc Welding) Electric Company - they have excellent materials that describe the various welding processes and the prices of their publications only include publishing costs, i.e. they are not looking to make a profit. They want to disseminate info on the current state of welding. Two of the books that I have bought from them are entitled "Metals and How to Weld Them" and "The Procedure Handbook of Arc Welding"; another Classic that I have of theirs is by Omer Blodgett "Design of Welded Structures". I know many structural and mechanical engineers that have the latter in their collections and they are all well worn with use.
RE: Welded Gusset Connection
One problem, though, is if you concentrate all the gap on one side, using a 3/8" strip, you introduce eccentricity into the connection. On the other hand, if you split the difference, all you have are 3/16" strips which are smaller than the originally specified 5/16" weld.
On the other hand, if the 5/16" weld was called for because that's the minimum size required by AWS because of heat issues (D1.1 Table 5.8), and not required for strength, then I'd go with the 3/16" strips if a 3/16" fillet will suffice for strength. You need to look into the fatigue category at the end of the strip and decide whether to just do longitudinal welds or wrap around the end; what did the original detail call for?
For the welds already made, take a look at Figures 3.3 and 3.4 in D1.1. Maybe one of those configurations applies.
If you don't want to go the strip route another possibility is to bevel the slot and make a real PJP or CJP instead of the fillets.
I'm not aware of any AWS restrictions on maximum fillet weld size. If you're worried about melt-through, use a low-heat-input procedure with multiple small passes to avoid a big molten blob all the way through the gusset thickness.
Hg
RE: Welded Gusset Connection
RE: Welded Gusset Connection
Of course making him increase the weld size will encourage him to be more careful in the future.
RE: Welded Gusset Connection
1. Get enough weld into the slot that they will be able to do a fillet, and then do a fillet with increased size. The weld deposited inside the groove wouldn't be counted for strenght purposes, just something to allow the fillet weld to have the proper profile.
2. Declare the whole thing a groove weld rather than a fillet weld and prep the joint accordingly.
Hg