moment welds. 1

[bb29510]

Doing a three story red iron bldg, they are hanging this week. Its loaded with moment welds, every connection. The weld is a B-u4a which is basically a groove butt weld unlimited thickness with a 45 degree and a 1/4 inch root, with backing. My question is, since the whole bldg is moment, how are they going to maintain the 1/4 root. I'm on the betting side that they are not going do it. Start complaining like contractor do and say its not possible. I'm asking because I can already see the fighting begin.If one column is out of measurement, then the 1/4 be out. please advise

master ICC inspector, AWS CWI

 

[dhengr]

Bb29510:
A good detailer/fabricator will have paid some attention to any tolerance buildup, plus or minus, in a string of beams and columns. He knows their shop practice and tendencies from experience. And, the erector should a thinking a column or two/three ahead as he erects that grid line of beams and columns. Obviously, the columns should be properly located and plumbed and the beams be fit btwn. them, with minor adjustments as they move down the line. The welding detail would seem to allow enough throat/root variation for this fit-up and for a good welder to do a good weld. A slightly larger root will only cost them some time and weld filler, it shouldn’t make for an inferior weld. You could always spec. 3.5" wide backer bars to give them a little extra leeway.

 

[BUGGAR]

I'm not sure of your configuration but ideally the erector has some beams on hold with the fabricator pending field measurements as "take up" elements to allow for erection tolerances. These should be identified on the shop drawings.
Let us know what happens.

 

[hokie66]

Won't you have bolted erection seats on the columns? The fabrication of the bolted connections tends to force the correct geometry.

 

[racookpe1978]

I have also seen root gaps "buttered up" (overlaid with one of more layers of weld metal to close up the gap) BEFORE making up the final weld root gap between the two parts. This should be done before fitup with the buttered metal inspected and ground clean and to shape; but almost certainly, there are many thousand real-world joints out there where the "field weld" was actually just a "fillet and fergit" made up by using enough weld rod to fill up the gap using the backing metal and filler rod to span an excessive opening.

SHouldn't happen, but you have to look at your field supervision, field weld inspector, and field engineer to make the joints properly. .

 

[gtaw]

The erector should plumb the interior columns and start welding the interior column/beam connections first and progress toward the outside edge of the building. Each joint will experience about 1/32 to 1/16 inch shrinkage as the weld contracts as it cools to ambient temperature.

AWS D1.1 includes as fit up tolerances that should be adequate to accommodate the contraction, i.e., the erector can open the root slightly in anticipation of the contraction.

The bottom line, the detail assumes a 1/4 inch root opening while detailing the connection. The erector opens the root to about 5/16 inch with the assumption he will loose that extra 1/16 inch once the weld is completed and cools to ambient temperature. The 1/16 contraction is an assumption that works for joints that are up to about 3/4 inch thick. More allowance should be considered for joints that are thicker.

The allowance can be adjusted once a few joints are welded. If the erector knows what he's doing, he will monitor the first few joints to make the necessary corrections in his root fit up allowance.

Best regards - Al

 

[bb29510]

Had a meeting with the erector today, after looking at the steel, the fabricator was nice enough to slot the bolt holes about an extra 3/8 so they is some slack for adjustment. The steel erector today told me, he has done many of the bldgs, and he wasnt going to comply, he was just going to weld up the joints, no matter how much root is there. He claims that what the backer is for from zero root to over 1/2 inch root he as just going to weld it up. I have a RFI to the project engineer now.

master ICC inspector, AWS CWI

 

[gtaw]

Stupid is as stupid does. Some people learn from their mistakes, others never do.

Best regards - Al

 

[wannabeSE]

Doesn't the B-u4a have +1/4, -1/16 fit up tolerance? What's the problem? Why can't the erector meet this?

 

[gtaw]

It is usually a case of the fabricator cutting the beam end twice and the beam is still too short.

There are provisions in D1.1 for root openings in excess of the dimensions shown in figures 3.3 and 3.4. The issue is the erector would actually have to have a copy of D1.1 and read it to find out how to address the situation correctly.

The other side of the coin is when the root openings are too tight. The erector can open the root up, but a little care and expertise is required so as not to gouge the heck out of the column flange.

The third party inspector should not get involved in telling the erector how to erect steel, how to weld the joints, or how to correct a deficiency. The TPI should simply report the nonconformance to the Engineer. The TPI is not the erector's consultant. The TPI represents the Owner. Ultimately, directing the erector only gets the TPI into very hot water.

Best regards - Al