Weld symbol 5

[WARose]

I've got 2 HSS sections (of the same size) I'm piggybacking on top of each other. I'm connection them by welding them along their lengths where they meet. What you would essentially need are 2 flare welds.......but I'm not sure I've seen a symbol like that before. Any ideas?

 

[Lion06]

JAE - The way I read that is that we, as the EOR, are designing the connection by showing plate sizes, effective throat for welds, etc.. and by not showing a specific type of PJP or CJP we are communicating to the fabricator by note (a) under 3.1.2 that there are no restrictions on the type of PJP or CJP.

We're not relying on the fabricator to do any connection design or determine the required throat thickness, only to select a PJP or CJP of their preference with no restrictions.

 

[48v]

Lion06, As per D1.1 2.2.5.3 either way is acceptable. At a minimum, the contract documents are required to show PJP or CJP. Anything further is up to you to specify or leave up to the contractor, including weld size (code minimums will apply if you don't specify) and groove type.

 

[dhengr]

To Nutte’s question, page 6.... Yes I could be confident of getting a .5" effective throat out of that 3/8" v-bevel. It has to do with the welding process and methods that the fab’er. uses to make the weld. One of those processes is sub-arc welding (SAW). Some weld processes penetrate much deeper than others, and the older codes would allow you an extra 1/8 or 3/16" of throat in recognition of this deeper penetration. I used this extra throat often in design, and sectioned plenty of them to know it can be true. I never really pushed my weld stresses to much, unless doing so would save me a weld pass or two. You also wanted good fit-up so you didn’t leave what is almost a crack starter at the base of the root pass, at the land. And, you certainly don’t want tensile stresses across that weld at the root.

That flare bevel is notoriously a difficult weld to do and often an inferior weld. The base of that root often looks like really bad chicken sh.t, with poor penetration into each wall, and no sound bridge btwn. them. The welder is trying to do both, and ends up doing neither very well. We often did that weld in two steps: we used a finer wire or rod for the first pass (or first couple passes), and a quicker freezing process so that you could build that bridge, and get deeper in the groove; then you could switch to a regular welding process to fill the groove. Fit-up btwn. the two HSS’s is another problem as pertains to the groove depth and width, thus the first couple passes can be fairly finicky. Another thing we used to do with a weld like that, and you probably won’t find this in the codes; we would press a small dia. soft wire down into the groove, almost as a backer bar, to start to build that bridge. Then the two step process may not be needed. We had welders who could melt the top 2/3's of that wire into the weld puddle, and leave the back of the wire generally a nice smooth backer. I don’t know the last couple eds. of the codes very well, but 48v’s “5/8R, 3/4R, and 1/2R respectively,” sound about right, depending upon the exact make-up of the joint. JAE’s sketch shows about the same thing as a function of welding positioning and penetration potential. And, I think they take account of the fact that I might not know the welders or the shop doing the welding, and as we are more and more want to do, they codify everything.

 

[nutte]

Dhengr, when I look at the AWS tables for prequalified PJP welds, all of them show the effective throat E to be either S or S-1/8" (where S is the groove depth). None of them show E to be greater than S. I'm not saying there isn't some penetration into the base metal below the groove depth. I'm talking about groove depth and effective throat call-outs on the weld symbol.

 

[48v]

Nutte, no prequalified welds have a weld size greater than the depth of preparation, but you could qualify a procedure that did provided you can prove the veld size with the macroetch.

 

[dhengr]

Nutte:
I don’t doubt what you are saying, I see that same thing in my older Eds. of AWS. I don’t know about the last few Eds. of AWS and AISC well enough to comment on the rationale for all of their changes in design stresses, tabulations and prequalified welds, etc., since I was last doing weld design every day. Most weld processes would limit you to a throat of ‘S’ or less, the groove depth or less. That was std. when I was practicing on a regular basis also. But, it was also common to some industries and codes to allow the use of the actual throat for design, once you proved you consistently achieved that grater throat. So, in practice we could to take advantage of the improved penetration of some weld processes, on some types of joints, and your ref. to Mike’s page 6 would have been one of those, as I remember it. Of course, this was contingent upon good quality welding, good fit-up, attention to detail, etc. I would not allow tension across that weld, at the root.

Finding this was like pulling teeth. I found some discussion on this actual throat vs. effective throat (or theoretical throat) issue, in several older AWS Welding Handbooks, and some Lincoln literature and Handbooks, but was not finding it in AISC or AWS manuals or codes. And then, finally a lead from some Lincoln lit.... in the AISC manuals:
7th Ed., sec. 1.14.7, Effective Areas of Weld Metal, can add .11" to throat size for SAW
8th Ed., sec. 1.14.6.2, do.abv.
9th Ed., ASD, sec. J2.2.a, do.abv.
1st Ed., LRFD, sec. J2.2.a, do.abv.
Don’t know after these Eds. what happened in AISC, and can’t find it in AWS
And, I think AISC was being safe/conservative with the +.11" added throat. I allowed this same design criteria on a groove weld (PJP) as long as I wasn’t dealing with tension across the weld, in which case I would not use the PJP weld. Someone above mentioned a convex top on the weld to increase the throat, but that is not allowed to be considered, at least I never did. I figured my throat to the theoretical surface of the weld and still always wanted the convex finish. Many times, to pick up throat size, I would detail a 1/8 or 3/16" bevel on the web pl. on a built-up girder, and the like. We could nibble or grind these bevels almost as fast as one of the guys could walk down the edge of the pl., that is, fairly min. extra prep. work to pick up that extra 1/8 or 3/16" (plus my .11 to 3/16") for root area penetration. I doubt that most Structural Engineers on bldgs. would go to this trouble, but for the most part we were always doing the design, piece detailing and the fab’ing., and I would actually ask for specific welders for some details, because I knew what they could or would do.

If I were designing today, either bldgs. or bridges, with the job to be let out to anyone who owned a welding machine, and offered a low bid, I’d probably use S - 1/8" too. I suspect the current codes account for a very competitive fab. market, not knowing who’s going to be welding it, fast and min. cost fab’ing., the fact that some grooves are tough to access with some processes, thus inferior root, etc., and this might be left to the fab’er. to determine. However they’ve screwed around with design stresses and the phi, phy, and pho-phum factors, the way welds work and the general engineering concepts involved in weld design really haven’t changed, just because they’ve changed the codes. A new name for an old concept is always a good way to add confusion to the whole process.

48V.... if you are going to use “velds” you have to use ‘machrovetching’ also.

 

[nutte]

Dhengr, thank you for the feedback. That note you reference, in AISC section J2.2a, was last in the 3rd edition LRFD manual. It is not in the 13th or 14th edition manuals. But, it is for fillet welds, not groove welds. In the current manual, they say that an increase above the diagrammatic effective throat of a fillet weld can be used if consistent penetration can be demonstrated. So it appears it is still allowed for fillet welds, but they're making you hunt for the amount of the increase.