welding / pre-qualified joints TC-U4a vs TC-U4b

[boffintech]

Pre-qualified joints TC-U4a vs TC-U4b

TC-U4a no root face; has backing bar
TC-U4b has root face; no backing bar

Question 1: For the TC-U4b, the shop drawings give the root face as 1/8”. The AWS D1.1 as fit-up tolerance reads “not limited”. Not limited? Does this mean the root face can be 0 up to the thickness of the beam flange?

Question 2: The shops do not indicate “a” or “b”. I was guessing “b” because on the fabrication page for end of beam prep he gave a root face dimension, but could have guessed "a" because on the erection page the detail shows a backing bar.

I think the guy is mixing up the two prequalified joints. If he uses “b” he gets the root opening tolerance down to 0 and if he uses “a” he gets out of backgouging.

Question 3: Is it possible for the inspector to check the fit-up in the field with the given information?

 

[henri2]

Boffintech,

Reponses to your questions.

1. That is clearly not the intent. Because if the root face becomes the thickness of the beam flange, the weld becomes a square groove weld. [TC-L1b, T1 = 1/4" max]. Why don't you contact AWS for an intepretation? For all we know, it may be an error and something they overlooked taking care of. I recall them taking over 2 decades just to indicate the correct reference for "eye examination" in the index. Tht correct reference for "eye examination" has been 6.1.4.4 since the late 80s but for years they had it at 6.1.3.4 (probably from an early 80s edition).

2. Regarding this prequalified joint, the shop and erection drawings are not consistent. An error no doubt, which can be rectified. Is this for a beam-column moment connection; beam flange joined to column flange? How often do you see them use TC-4Ub? They probably had TC-4Ua in mind.